This isn't a particularly serious or big bug, just something I've noticed that I'm sure could be fixed quite easily in the next Vavoom release.
In the game Heretic, if you step in, fire your crossbow into, or explode one of the, umm... explodey ball thingys near "goop" (the watery/poison looking stuff that hurts you if you step in it), it seems to create a little splash particle/sprite (whatever you want to call it) that takes a fair amount of time to disappear... looks like a little floaty thing in the water there.
The bug seems to be that because that little "splash" thing seems to be staying longer than it should, if you get a whole bunch of em in the same area, it slows down the game tremendously. Not enough to crash the game (not yet at least), but enough to slow it down for a significant period of time. However, after a while, the slowness goes away (the "splash" things stop).
My description of this bug was probably not the best, but you can easily see for yourself. Simply fire up a game of Heretic, go to level 2 of the first episode and go to the poison water near the blue key door (or anywhere else you can find poison water). Fire into the water with your crossbow (or any weapon that isn't a scan-hit weapon such as Phoenix Rod, Hellstaff, etc..) to create these "splashes" and after a bit, you'll start to notice the game slows down quite a bit because the "splashes" won't go away for a fair while.
If you need further information, let me know. I'll check back here after a bit to see if you require more.
edit: If it's of any help, when I started these "never-ending splashes", I opened the console and got the following warning:
"Warning! can't find sound world/sludgegloop"
This message seems to have been written over and over, much like what these "splashes" seem to be doing.