I don't doubt you'll be able to find decent replacements for the usual apps: word processing, dvd burning, an MP3 player... but the devil is in the details as they say. What if you need something specific like say... an MP3 ID3 tag editor? Or DVD decryption software? Or a particular IRC client? Or a mac-compatible codec? That's one of the reasons why I don't use linux full time: you have to figure out a ton of things for yourself, and it's not always easy.
Having said that, if you're willing to endure some of the mac's quirks and software hurdles, you really can't go wrong with one. I've heard nothing but good things about them.