I have been using doit for roughly half a year now, practicing GTD for quite a few years and using a number of different applications as my trusted system.

I like Doit for its availabilty on multiple platforms and a robust and efficient cloud sync, while it is an easy to use and pretty clean GTD implementation.

One thing which I am missing however, which I had in a tool I was using before, was a Tickler functionality, which was implemented the following way:

On items in the someday-maybe list, you could set a 'tickle-date' once this date arises, the item will automatically be moved from the Someday-maybe list and into the Inbox. To me this prooved a very nice feature eliminating to frequent reviews of my messy someday-maybe lists, as I could always trust the items being brought to my attention on the tickle date.