I have a fresh install of wordpress 3.3.1 on a new VPS, running buddypress (no groups or group forums), but I'm using the bbPress forums.
The site went live 2 days ago. Yesterday, I decided to try this plugin (Activity Plus), so I installed and enabled it, with no problems.
A couple of hours later, I decided to try posting an image from my computer. I uploaded the image, and the Ajax uploader got stuck at 72%. Eventually, I tried to refresh the page, but it wouldn't respond... I couldn't even log into my WHM account for the VPS. I had to reboot the server, and even afterwards, there were lingering problems (my site could no longer connect to Akismet or the WordPress plugin feed).
After sorting these things out (and having disabled the plugin), my site was fine all day. Fine enough, in fact, that I decided that it may have just been a coincidence that my VPS crashed at the same time that I tried to upload an image with that thing. So, I tried it again.
Unfortunately, the result was the same. Server freeze, reboot, and a variety of problems (the same ones as last night, though... not random data corruption problems from a hard reboot).
Beyond buddypress and bbPress, I have a minimal set of plugins installed.