Very poorly? I couldn't disagree more. It's not as elegant as iPhone, but it does many things very well and in a vastly more powerful and customizable way, even at the most basic level, like calendars, email and phone usage. Nearly every feature ppl complain that the iPhone is missing is available and works for WM.
I had difficulty for the first few months with active sync, but then it worked perfectly. It was capable of syncing much more info than apple does. Other than Outlook? iPhone doesn't even do outlook or entourage syncing well, let alone lotus. With regard to documents, of course it's cumbersome to do on a small phone, but the point is that the capability is there if and when you need it. Plus being able to make a small edit and send a document back was huge.
I ran many solid programs, had lots of registry edits, and I had more crashes with iPhone in two months than I did with two plus years of WM usage.
I never had a complete failure of either my treo 700w or wx in two plus years.
The only thing I had similar to that in WM was the daylight savings bug, which was a monster of a problem.
I was also hesitant about iPhone initially, and it does keep things in sync across multiple platforms more consistently than active sync was capable of doing.