Have any of you experienced the following, and have you found a solution:

A large part of our website's back-end is MS SQL Server 2005. Every week or two weeks the site begins running slower - and I see queries taking longer and longer to complete in SQL. I have a query that I like to use:

USE master
select text,wait_time,blocking_session_id AS "Block",
percent_complete, * from sys.dm_exec_requests 
CROSS APPLY sys.dm_exec_sql_text(sql_handle)  AS s2 order by start_time asc

Which is fairly useful... it gives a snapshot of everything that's running right at that moment against your SQL server. What's nice is that even if your CPU is pegged at 100% for some reason and Activity Monitor is refusing to load (I'm sure some of you have been there) this query still returns and you can see what query is killing your DB.

When I run this, or Activity Monitor during the times that SQL has begun to slow down I don't see any specific queries causing the issue - they are ALL running slower across the board. If I restart the MS SQL Service then everything is fine, it speeds right up - for a week or two until it happens again.

Nothing that I can think of has changed, but this just started a few months ago... Ideas?

--Added

Please note that when this database slowdown happens it doesn't matter if we are getting 100K page views an hour (busier time of day) or 10K page views an hour (slow time) the queries all take a longer time to complete than normal. The server isn't really under stress - the CPU isn't high, the disk usage doesn't seem to be out of control... it feels like index fragmentation or something of the sort but that doesn't seem to be the case.

As far as pasting results of the query I pasted above I really can't do that. The Query above lists the login of the user performing the task, the entire query, etc etc.. and I'd really not like to hand out the names of my databases, tables, columns and the logins online :)... I can tell you that the queries running at that time are normal, standard queries for our site that run all the time, nothing out of the norm.