I've been testing Hyper-V lately and thought of compiling a list of things which are either incompatibilities, issues or "bugs" with Hyper-V.
Note: This is what I have experienced personally or from the field and is never a complete one. I'll be updating it as and when new information is available.

1. All roles except DC (Domain controller) role is supported
2. If you are using virtual switches in a VM cluster then make sure they are identically named on both nodes. Make sure you have installed integration services before attempting a failover. I also noticed that creating virtual switches using the GUI during installation doesn't cut it and you need to delete it and recreate it again to make it properly work inside a cluster
3. Since, we are dealing with pre-release material here and one thumb rule is, don't expect everything to work straight forward. For instance, upgrading a VM configured on Hyper-V pre-beta code (RC0) to Hyper-V Beta RC1 may not be supported and may offer un-predicatable results.
4. Always install the virtualization integration components for Linux inside Virtual Guests. Otherwise, you won't see the devices. The Linux downloads are available from Connect Website 
5. While enabling Hyper-V role, make sure you keep (do not change) EN-US as your default language otherwise you may get VMM service failures and Hyper-V wouldn't start
6. Wireless network adapters on laptops are not supported by Hyper-V.