I don't think basic system administration of Solaris 8/9 shouldn't be too much of a learning curve. Most differences can be handled by the rosetta stone (http://bhami.com/rosetta.html).
Solaris 10 has a lot more differences, but the only one you would *need* to learn about is the Solaris svcs stuff, which has taken over Solaris init scripts (Think DJB's daemon tools for everything).
There are big differences in how the Solaris kernel runs that you should know about for performance monitoring, the most notable being in the way it handles memory. Solaris doesn't free up any more than 3 or 5% of memory, so the only reliable way to monitor your memory usage is to watch for scanrates. On Solaris 8+, if the system scans then the system has run out of memory-- otherwise, it hasn't (there are other rules for S. 7 and lower)
That being said there are a lot of additional features in Solaris that you may want to use, like: * Role based access control (introduced in S. 9) * Resource Manager (limiting a process's CPU usage-- introduced in S. 9) * Solaris Zones (process isolation + chroot to emulate of multiple OS's-- introduced S.10) * DTrace (process instrumentation-- introduced S.10)
These require some study to implement, but you can run a systems without knowing that they exist.
HTH Aaron