Hi!
I'm using and administrating Novell NetWare since version 2.2 and the latest NetWare 6.5 SP3 is identical with OES (with NetWare kernel).
I'm using both here, NetWare 6.5 for File and Print, SME for Mail, News and other Linux services.
In the future I may switch to the Linux version of OES, because Novell offers the NSS filesystem and the much better file access management on Linux, too.
NDS or eDirectory makes much sense with two or more servers, since all users, groups and other objects are automatically synchronized between servers.
Many other services like iFolder, ZENworks, GroupWise are already supported under Linux, so if you need these services, it may be good to switch to OES. Otherwise you may stay with SME.