I would say my original Droid lasted for the longest time, and replacements fail daily.
Original Droid: 8 months (Touch screen no longer responsive)
1st Replacement: 1 month 4 days (Too mane dead pixels)
2nd Replacement: 1 month 1 week (Volume up key no longer functioned)
3rd Replacement: Just got it yesterday.
I am assuming replacement will last about a month as well.
The worst part is each Droid I get, I customize less and less because I feel as though it isn't worth the time know I will just have to send it back eventually anyways.
So how long have your Droid replacements lasted?