For a few weeks now, smartd has been reporting that it is skipping some of its scheduled self-tests on the weekends:

Apr 24 18:29:32 calvin smartd[4758]: Device: /dev/sda, skip scheduled Offline Immediate Test; 40% remaining of current Self-Test.
Apr 24 18:29:33 calvin smartd[4758]: Device: /dev/sdb, skip scheduled Offline Immediate Test; 50% remaining of current Self-Test.

The drives in this RAID-1 array are set to run an offline test four times a day, a short self-test at 2am every day, and a long self-test on Saturdays at 2am. For some reason, it looks like the long self-test is taking longer, causing the other scheduled tests to be skipped.

First question: is this a sign of likely drive failure?

Then today, smartd reported that a self-test failed. Here is the output of smartctl -a /dev/sdb:

smartctl version 5.38 [i686-pc-linux-gnu] Copyright (C) 2002-8 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

=== START OF INFORMATION SECTION ===
Model Family:     Seagate Barracuda 7200.8 family
Device Model:     ST3250823AS
Serial Number:    3ND1GNBC
Firmware Version: 3.03
User Capacity:    250,059,350,016 bytes
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   7
ATA Standard is:  Exact ATA specification draft version not indicated
Local Time is:    Sun Apr 25 13:15:34 2010 EDT
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status:  (0x82) Offline data collection activity
     was completed without error.
     Auto Offline Data Collection: Enabled.
Self-test execution status:      (   0) The previous self-test routine completed
     without error or no self-test has ever 
     been run.
Total time to complete Offline 
data collection:    ( 430) seconds.
Offline data collection
capabilities:     (0x5b) SMART execute Offline immediate.
     Auto Offline data collection on/off support.
     Suspend Offline collection upon new
     command.
     Offline surface scan supported.
     Self-test supported.
     No Conveyance Self-test supported.
     Selective Self-test supported.
SMART capabilities:            (0x0003) Saves SMART data before entering
     power-saving mode.
     Supports SMART auto save timer.
Error logging capability:        (0x01) Error logging supported.
     General Purpose Logging supported.
Short self-test routine 
recommended polling time:   (   1) minutes.
Extended self-test routine
recommended polling time:   (  84) minutes.

SMART Attributes Data Structure revision number: 10
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x000f   047   039   006    Pre-fail  Always       -       168450357
  3 Spin_Up_Time            0x0003   098   098   000    Pre-fail  Always       -       0
  4 Start_Stop_Count        0x0032   100   100   020    Old_age   Always       -       33
  5 Reallocated_Sector_Ct   0x0033   100   100   036    Pre-fail  Always       -       9
  7 Seek_Error_Rate         0x000f   087   060   030    Pre-fail  Always       -       654745480
  9 Power_On_Hours          0x0032   055   055   000    Old_age   Always       -       40141
 10 Spin_Retry_Count        0x0013   100   100   097    Pre-fail  Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   020    Old_age   Always       -       51
194 Temperature_Celsius     0x0022   037   062   000    Old_age   Always       -       37 (0 17 0 0)
195 Hardware_ECC_Recovered  0x001a   047   039   000    Old_age   Always       -       168450357
197 Current_Pending_Sector  0x0012   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0010   100   100   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x003e   200   200   000    Old_age   Always       -       0
200 Multi_Zone_Error_Rate   0x0000   100   253   000    Old_age   Offline      -       0
202 TA_Increase_Count       0x0032   100   253   000    Old_age   Always       -       0

SMART Error Log Version: 1
No Errors Logged

SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Short offline       Completed without error       00%     40131         -
# 2  Extended offline    Completed: read failure       30%     40129         379795511
# 3  Short offline       Completed without error       00%     40084         -
# 4  Short offline       Completed without error       00%     40060         -
# 5  Short offline       Completed without error       00%     40036         -
# 6  Short offline       Completed without error       00%     40013         -
# 7  Short offline       Completed without error       00%     39990         -
# 8  Extended offline    Completed without error       00%     39977         -
# 9  Short offline       Completed without error       00%     39919         -
#10  Short offline       Completed without error       00%     39895         -
#11  Short offline       Completed without error       00%     39872         -
#12  Short offline       Completed without error       00%     39848         -
#13  Short offline       Completed without error       00%     39824         -
#14  Short offline       Completed without error       00%     39801         -
#15  Extended offline    Completed without error       00%     39789         -
#16  Short offline       Completed without error       00%     39754         -
#17  Short offline       Completed without error       00%     39732         -
#18  Short offline       Completed without error       00%     39707         -
#19  Short offline       Completed without error       00%     39683         -
#20  Short offline       Completed without error       00%     39660         -
#21  Short offline       Completed without error       00%     39636         -

SMART Selective self-test log data structure revision number 1
 SPAN  MIN_LBA  MAX_LBA  CURRENT_TEST_STATUS
    1        0        0  Not_testing
    2        0        0  Not_testing
    3        0        0  Not_testing
    4        0        0  Not_testing
    5        0        0  Not_testing
Selective self-test flags (0x0):
  After scanning selected spans, do NOT read-scan remainder of disk.
If Selective self-test is pending on power-up, resume after 0 minute delay.

Given that this drive is about 4.5 years old, I am probably tempting fate by keeping it in service.

SMART doesn't seem to get much respect as a reliable way to predict drive failure. What else can I use to get an early indication of drive failure?