I recently upgraded a couple of our systems from Samba 2.2.7 to 3.0.4 and noticed that connecting to shares of the form "\\server\service%username" appears to have stopped working. The man page still refers to this form of connection, but when I connect, I get NT_STATUS_BAD_NETWORK_NAME back. We still have quite a number of Windows 98 clients whose users login under a different username from that used on central systems. This is going to be a problem if I roll out the upgrade onto the production systems. We also have a similar need on our Windows 2003 Citrix servers - if they connect all users to "\\server\temp" (where the samba config looks at the username and gives each user their own temporary space), then sometimes the servers appear to mix up who belongs to which connection. We solved this a couple of years back by using the percent hack to make the citrix server see each connection as having a distinct name (\\server\temp%auj). I hacked the sources to ignore everything after a "%" (by nulling it out around line 791 of smbd/service.c), and this works for the Citrix case. It won't, of course, solve the problem for Windows 98 users.
I think this is just one the causualties on the move from 2.2.x to 3.0.x. Marking this one later in case anyone wants to revisit it.