I am not entirely sure what information will make this bug useful, please advise. Essentially, whenever Parallels version 3.0 (latest build) is run with a nightly build of webkit, both Parallels and Webkit slow to a crawl. They initially seem to lock, but after a few moments Parallels continues and then later Webkit does as well. All applications on the system are slightly slower, but Webkit often becomes entirely unresponsive. I have a MacBook Pro (bought December 2007) with 2GB of RAM, and each OS gets 1GB when running Parallels. Neither Parallels nor Webkit takes up excessive CPU time according to the monitor, but they both take a huge hit. I suspect that they are somehow blocking each other's network calls.
I'm not seeing anything abnormal in a similar configuration. Of course, there are a lot of delays due to swapping memory to disk and back - you can use /Applications/Utilities/Activity Monitor.app to check for it. From personal experience, I think that giving Parallels 1 of total 2 Gb of RAM is excessive - I' m getting better results with 512 or 768 Mb. But that's really off-topic here.