I have had a few Pioneers. 2400Bt, a 2500BT, and now a 501EX. I stuck with them for awhile because if I felt like upgrading for several years all I had to do was pop the dash open, unplug one unit, and plug in another. I'd usually pick up an older model on its way out to get whatever features I didn't currently have that I decided I wanted. This last time I found out once I had the dash open that they changed the shape of the power plug at some point so I had to run back out to get a harness and make all the connections. No big deal, I went ahead since I was already committed and had everything un boxed. But I might have taken my time and looked at other head units if I knew ahead of time it was no longer a simple plug and play swap.
Regardless, the Pioneers always seem to pack a little bit more features for the money than the other manufacturers. I just wish their hard buttons were as user friendly as everybody else's.