In case you have problems with Unbirth crashing for no reason from time to time during area transition:
- right click on unbirth.exe and open "Properties",
- open "Compatibility" tab,
- check "Launch this program in mode compatible with:",
- select "Windows 98 / Windows ME"
Exact text may be a bit different as I'm using non-english Windows here. It seems that the above solved all problems with Unbirth crashes for me - at least it didn't crash so far, while it used to do a lot, so it's possible to play it now.
Have fun!
P.S. to developers: Maybe it's worth putting this notice on Unbirth site?
EDIT: Well, it almost fixes all problems (the game still may crash), but at least improves stability considerably.