I had a lot of trouble with HTC Sync with Outlook and my Evo. Then someone mentioned that Microsoft's ScanPST utility had helped them:
How to find and run the Inbox Repair tool in Outlook. It took several runs, but my PST file errors were finally fixed, and HTC Sync worked much better.
I still have a relatively small problem where some of my most used contacts get switched to first name, last name in Outlook. Other than that, it's been pretty solid.
A more major problem for me is Google's inability to handle variations in recurring calendar events. As this Google forum thread shows, it was first reported in March, 2009 and still hasn't been fixed:
Issue 2229 - android - Calendar: Deleting one instance of a recurring event (excluding), results in duplication of it. - Project Hosting on Google Code