Read the "perl58delta" document in the 5.8.x distribution. It will tell you what's different, in roughly descending order of possible problems. And if you go for 5.8.1, 5.8.2, etc. you should also check "perl581delta", "perl582delta", etc.
PS: You should be sure it's 5.8.1 or later if you're interested in safe signals, because 5.8.1 supports safe and unsafe signals with a command line option, as well as through POSIX::sigaction. Older versions could only do unsafe signals through sigaction. (I know this because I submitted the sigaction patch. :-))
OTOH, there's no reason not to get 5.8.3 anyway...
-- Chip Salzenberg, Free-Floating Agent of Chaos