I will have to deal with some Solaris machines in a couple of months, but I am a born and raised Linux admin (since like, 1997). Even so, Unixes are Unixes and even if they have their differences, many things are easier to grasp.
What I would like are resources and tips from the Server Fault community about the most critical/different points so I can focus on learning those.
I already have: Solaris to Linux Migration (IBM Redbook) and Linux to Solaris Administrators Guide (Sun). Any tips are welcome :)
It depends if you are maintaing a Solaris 10 machines or the older ones (9,8). For solaris 10, some of the commands are almost the sames with Linux. If you are a bit unlucky like me you need to dig more for Solaris 8 and 9 commands, which makes a lot of different.
Important areas from my point for administering the box for Solaris 10 that a Linux Admin need to know are:
Other than that... read LKSF book by Joerg Moellenkamp.
I like the Unix Rosetta Stone - http://bhami.com/rosetta.html Also covers other flavors of Unix.
System Administration Quicksheets (in PDF) - http://www.tablespace.net/quicksheet Solaris PDF is good. Talks about basic tasks (mirroring, hardware) and includes some of Solaris 10's eccentricities.
Solaris Tips and Tricks - http://sysunconfig.net/unixtips/solaris.html This one has some OBP stuff too which is quite handy.
It is a good kick-start: http://www.sun.com/software/solaris/sysadmin_guide.pdf
And a brief introduction to Solaris: http://www.cuddletech.com/blog/pivot/entry.php?id=562
An FAQ for folks coming from Linux: http://hub.opensolaris.org/bin/view/Community+Group+documentation/newbie_faq