I had a problem with my LG E900 WP7 phone over the weekend, Outlook stopped synchronising with our office Exchange server.
It started when I got back from a trip Ireland. My phone switched back from roaming and started to use 3G for data again, as opposed to WIFI. Also over the weekend we had a connectivity problem from the office to the Internet so for a while I could not connect to any of our services from any device. However, even after both these things were sorted my Outlook still failed to sync, it said it was in sync but showed no new email since Friday when it was disconnected from my Irish ISP based MIFI in Ireland. No errors were shown. I waited until I got back to the office and tried a sync via our internal WIFI, all to no effect.
The fix was simple, and obvious, delete the Outlook account on the phone and recreated when I was in the office. Problem is I still have no idea why this issue occurred.
So that is 2 issues in about 6 months, much better than my previous few phones!