I do my own with Turbo Tax (my credit union gives me an online special and helps automate some things) but I don't suggest it if you itemize unless you know exactly what you're doing... Which is tough because even the IRS doesn't seem to know what to do. Then again, there was s study a while back where something like 40-50 professional tax preparers were all given the exact same financial setting and asked to prepare the federal taxes. No two returns came out the same, and not sure if any of them were actually correct. And when you call the IRS for help, I think their record is around a 20% chance of getting the correct answer. It's been a while since I heard about those two studies and running off memory, so my numbers may be off but the results were dismal regardless.
Down with the IRS, Fair Tax now. Then we wouldn't have to deal with all those hassles.
Edit: For those using professionals, keep in mind if they make a mistake and you get in trouble, you're still the one on the hook as far as the IRS is concerned. When you sign off on your taxes, you're signing that you affirm everything is true and correct (*chokes back a laugh*), and it doesn't say anything about your preparer accepting or being assigned fault for mistakes.