1. Why can't you only remove the VDI PC from the broker (and leave it in vCenter) when using linked clones persistent pool, when it can be done with non linked clones (fat)? For reasons why this is bad, see http://communities.vmware.com/message/966551#966551
2. Related to 1 I guess. Please make it possible via GUI to (re)assign the user<->PC relationship in a pool. Both with fat and linked clone VDI PCs. For reason, see link above. I would dislike having to set up individual desktops for all, it does not scale well to say the least..
3. Please make it possible to use Windows Server 2008 (32 and 64 bit) as all roles with VDI (broker and composer).
4. Please make it possible to use 64-bit XP/Vista as VDI clients.
I can check as to why but more than likely it's because it's a persistent pool and the idea is one VM per user in a persistent pool.
For a non-persistent pool it makes sense to be able to use more than that because you're not tied down. I would highly recommend, however, that you put in a feature request.