I too have had extensive problems with Activesync in the past. My problem was that Activesync would only work after a fresh reboot of Windows. If I left my Ax in the cradle after syncing once, it would never resync on its own again until I rebooted. I tried soft and hard resets, un and reinstalling Activesync 3.6 (I'm using XP), disabling firewall, uninstalling McAfee firewall and installing Zone Alarm, checking and reconfiguring Ax settings, and even getting a replacement Ax but NOTHING worked (at least permanently).
At first I thought it was DSL related because I started having problems about the same time I switched over from dial-up to DSL. In retrospect, I now realize that it had to do with hiccups during the syncing process, especially during the installation of new programs. I came to this conclusion because I found that after I got my replacement Ax and everything seemed ok, the problem started again once I tried reinstalling some programs. If I got errors during the installation process, or the application hung, my syncing problem would recurr. However, when I tried system restore to a time where Activesync was working normally, the problem was fixed. This makes sense in relation to my switchover to DSL since it was also at that time I started downloading extensively and trying out new applications.
Anyway, to sum it up, I have concluded that my Activesync problems are not due to problems with the Ax itself but to Activesync on my PC. It doesn't seem very "robust". Also, the best solution I have found to this problem has been to use
Resync. It has worked like a charm for me!!!