Same for me, 3.3.1 is the only version that never failed on the one machine I used it on for weeks. On another machine I updated regularly from 3.4.n through 3.6.4 and always got at least one zombie after a day or so (no big deal) or problems that were much more severe, particularly with 3.6.4. Symptoms have varied but often include loss of Internet access (of all things) which often (but not always) returns if I shut off cgminer. Causality seems very murky and I know my comments are anecdotal only. I'd guess that a memory leak has crept in some time after 3.3.1 but I've done no testing along those lines.

I've discovered that the machine that was stable on 3.3.1 also becomes unstable on 3.5.n and up, which is the main reason I'm posting this. It's not a complaint, but perhaps it will be a useful clue to some obscure issue.

Both machines are core i7 64 running Win7 64. Both use a bunch of erupters and one has a BFL LS as well. At first I thought the instability was caused by the heavier load on one machine but now I'm pretty sure it is not load-dependent.