I've used Turbo Tax for about four years now and agree it's fairly idiot proof.

I will say that they kind of screwed up my state taxes this year though. Some Indiana counties had some property tax issues that resulted in a tax rebate issued in 2008 for taxes that were assessed in 2006 and payable in 2007. Turbo's calculation for the deduction I was able to take this year was very overstated. After reading the state's instructions repeatedly, I could only conclude that the program was wrong. I ended up doing my state taxes on my own.

So, while I think these programs are very helpful, if something doesn't look right, you should double check the calculations.