Why do you use 37Signals products? Simplicity, UI, Hype?

After watching various videos and seeing the growth of 37 Signals, it makes me curious why people use their applications. They clearly have less features and I don't see that as a large issue. Since they are mostly designers you would expect the UI/UX to be good. Finally I'm sure that some just jumped on their products because of the RoR hype. So if you use a 37 Signals product, why do you continue to use it?