It's going to be interesting to see what happens when 4E releases.
If it's a radical change that nullifies the value of my current collection, then it had better be as good as the change from 2.0 to 3.0 to make me follow. I'd be very impressed if that were to happen.
Reading some of Monte Cook's comments about design of 3E has been very enlightening - especially his discussions about D&D "icons" if you will, such as hit points, 3-18 ability score spread (vs. just +1, +2, etc.), magic missile always hitting, etc.
If those icons were to go away, and I no longer feel connected to the game that sparked my imagination all those years ago as a 10-year old kid, then I will most-likely not play a new edition.