First of all, I recommend reading Don't Just Roll the Dice if you haven't already: http://www.scribd.com/doc/25050778/Dont-Just-Roll-the-Dice-P...

This was talked about earlier today (http://news.ycombinator.com/item?id=1613852). Unless your app requires a whole pile of non-paying users for network effects, free accounts don't seem to bring in much value. If you want customers who are going to pay at some point in the future, trials seem to make more sense than perpetually free versions.

You could of course try running without a free plan to start, and add one if no one's taking you up on the free trials. But for those people who use the free trial but walk away without signing up, I doubt a free version would have resulted in a future conversion from them. More users equals more support; free accounts could destroy your business.