i just moved to computer audio and went through the same decision process. was in the same position as you are. long time pc user debating if apple was the better route. ended up getting a very nice pc and could not be happier. for under $700, it was a no brainer compared to an apple product. what does $700 get ya??
intel i5 w/WIN7 64 bit pro
8g memory
2g graphics card
3T worth of high speed hard drive space
network/streaming hardware (router and ethernet adapter)
J River MC16
wireless keyboard and mouse
apple makes great stuff and if you're already onboard...it's a good way to go. however...if you're a pc person, i see no compelling reason to pay a lot more and change over to apple. with the intro of WIN7, the choice was made even easier for me. it's far and away the best OS microsoft has ever produced. miles ahead of vista and other problematic microsoft os's.
if you're like me and need a pc for home and work, switching to apple just for music makes little sense imho.