The sound crashing issue on 3.4 was something I worked around by changing our sound handling to a kid the issue. However, the unity editor is extremely crash prone in 3.4 to 3.5, and I didn't know what other problems there might be -- there were some reports of deadlocks on client machines because of the multithreaded rendering they added, so we opted to stay on the rock solid 3.3.
We have since bought version 4.0, but as Keith said the asset loading is mysteriously slow on some but not all machines. As in, 30 seconds to load valley 2 instead of 2-4. I never saw that on either of my machines, but Keith and josh both did. I've not had time to stop and send a bug report, and when I tried to make a super simple game that did nothing but load some small assets, it did not exhibit the problem. So it's clearly some really odd mix of issues, which is the worst kind to actually find. For the time being, since 3.3 is so solid and we actually have to get products out rather than helping unity fix bugs (that, in our past experience submitting 4 bugs, never were addressed anyhow), it's been a low priority for us. If I knew they would fix it that would be different, but they never addressed the other four bugs in two years. Sigh.