I have tried Basecamp mainly because I had heard about it so much on blogs, articles, etc. I had used AceProject for a while and I was curious about the "To Do" type thing in Basecamp. The interface simplicity is awesome, the way milestones are displayed is nice and it allows unlimited users, no matter which package you subscribe to.
However, I decided to get back to AceProject for several reasons. In project management, I think features like Gantt charts, task reports and time tracking are necessary. I feel Basecamp is like a giant "reminder" software. I did not find any access levels (admin, normal user, etc.), any reports, no data import/export... These features are all available in AceProject... and more! I need that.
The bottom line, Basecamp is not for me, thank you.