After signing up, all you do is upload your PDF and choose your desired output format: Word or Rich Text Format. The latter won't net you the best results, but Word conversions end up looking very much like your original PDFs.
Want proof? Check out Lifehacker's before-and-after comparisons. Me, I'm loving anything that lets me fill out a W-9 form in Word. (I also love stuff that's free, though I'm not sure PDF-to-Word will remain so after it exits beta.)
To get in on the beta-invite action, head to the PDF-to-Word site and use this code: BNET. (Tricky, huh?) It expires after 200 users sign up, so don't wait!