I have Lightroom and Photoshop CS4 on the iMac at home, but found myself needing something on my MBP from time to time to develop RAW, so I put Master on it. It's serviceable, but I don't really care for the workflow. Having said that, it does have some nice tools in it, if you know what you're doing. One, the "e-Portrait" has a "smoothing" tool that can clean up wrinkles, acne, et cetera, pretty well but be careful about application. Lighter is better. e-Portrait also has the ability to "enlarge eyes," which is a common technique of pro photographers.
Of course, in the last update to iPhoto, they finally put RAW support in it for the E-P1, so I'll probably not use Master now for anything other than firmware updates.
I use Olympus Studio on Windows XP... it means I can shoot raw and apply any of the Art Filters afterwards, plus I can get the Olympus colour signature as the starting point (I usually finish by applying my 'enrich shadows' style and any other relighting and scaling in Lightzone).
My next favourite is currently Capture One 5 PRO - with the Olympus colour signature provided by FujiCol... one of the posters over on dpreview who does custom icc profiles.