This is a very common problem; seen in a lot of different scenarios; but it’s most annoying on RDS / XenApp-servers.
Logon stalls on printer mappings; for all users.
Apparently this is due to the fact that for each printer; every user tries to download the driver from the print server. If you’ve got a bunch (especially HP printers in my experience), it’ll take a good while.
Luckily; there is a fix:
http://support.microsoft.com/kb/2853367/en-us?sd=rss&spid=14134
I haven’t tested this extensively; but if anyone gets the chance to before I do. Drop a comment!