In my current CruiseControl setup I am running the following target:

<modificationset quietperiod="30">
       <svn RepositoryLocation="http://my/url/repo/trunk" />
</modificationset>

I do a simple checkin of a blank text file and subsequently the messages I receive in the CruiseControl log are as follows:

[cc]May-13 15:53:56 Project       - Project mine:  bootstrapping
[cc]May-13 15:53:56 jectController- mine Controller: build progress event: bootstrapping
[cc]May-13 15:53:56 Project       - Project mine:  checking for modifications
[cc]May-13 15:53:56 jectController- mine Controller: build progress event: checking for modifications
[cc]May-13 15:53:59 Project       - Project mine:  No modifications found, build not necessary.
[cc]May-13 15:53:59 Project       - Project mine:  idle
[cc]May-13 15:53:59 jectController- connectfour Controller: build progress event: idle
[cc]May-13 15:53:59 Project       - Project mine:  next build in 1 minutes
[cc]May-13 15:53:59 Project       - Project mine:  waiting for next time to build
[cc]May-13 15:53:59 jectController- mine Controller: build progress event: waiting for next time to build

Tortoise: TortoiseSVN 1.6.8, Build 19260 - 32 Bit , 2010/04/16 20:20:11
CruiseControl: 2.8.3