There have been some rumblings around internet of users experiencing some issues regarding Contacts on their WP7 phones. While we haven't experienced them ourselves (Edit: our pal Paul Acevedo has), there seem to be two things happening.
Firstly, people are reporting that Contact tiles are pinned to the Start screen will randomly disappear. The contacts themselves remain on the phone, but the tiles get removed from the Start screen. While some of this could be attributed to an unlocked screen being put into a pocket, there are cases where several disappear at once.
The second bug involves linked contacts. When you have the same contact in two places, like email and Facebook, WP7 will automatically linked the two. Allegedly, users have seen these links broken in some cases, be it links made automatically by the OS or ones that have been manually created.
So far, this is all anecdotal, but there are enough cases being talked about that it could point to an actual bug in WP7.
What say you? Have you come across any of these issues on your WP7 devices?