Also, I noticed that the poclbm.exe process is now taking up 50% of the CPU usage, with the first of the 2 dual core CPUs at 100%, when it used to be 0% with the 2011-06-09 version of guiminer.exe.
I am having a similar/same problem. I have a cpu+nvidia mining going. Every 15-120+ seconds poclbm consumes a core (of 4) to 100% for around 30 seconds. poclbm has used 50min+ of cpu time in just the last few hours. I do not recall this happening on the previous version.
The impact on cpu mining is obvious.