Exactly, the whole point in a mac is the OS, the best known to man. If your getting the new Mac Mini, id use either Adium or aMSN as they have optimized binaries for intel cpu's, you could also have a look at fire, not used it myself though. Any more questions just ask, in sure me and Moria can answer them
I also ordered mine from the Apple shop, good service but the courier was wank (not Apple's fault of course) If your looking for something cheap the I'd avoid Apple, you pay for what you get after all.