Microdermabrasion has done more for my infrequent pimple breakouts more than any other acne medication or treatments combined. Just exfoliating that top layer of skin makes my face feel smoother, refreshed and cleaner. It is a little drying though, but nothing a little facial moisturizer can't cure. On top of that, it's relatively quick and painless!
However, microdermabrasion will only do so much. If you're thinking of getting micro done to diminish or eradicate fine lines and/or build collagen, you're much better off spending your $$ on a peel or laser resurfacing. As for overall skin tone and quality, religiously applying hydroquinone and retinoids has done way more for my face than microdermabrasion.
It's just another tool in my skin care arsenal, but I would never rely on it as a panacea for all my skin care needs.