This thread caused me to check weight. With rack, fenders, miscellaneous accessories, but no bags or day to day gear, my ride is about 35 Lbs. Adding my panniers packed for today added another 20 lbs, for a total loaded weight of 55 lbs. I know I have carried an additional 5-10 lbs of gear on occasion, but sometimes I go lighter, too.

I have to move the bike up and down short stairs daily, without panniers, and once or twice a week I have to do a full flight each way (also unladen by panniers). Today I rolled/ carried the bike out with the panniers, and the steps were quite a pain. I could not easily have loaded the bike on my car's bike rack with the panniers in place. Admittedly, the balance is part of this, with so much weight to the rear.

From this, I can conclude that 35 lbs is acceptable. 55 lbs is too heavy for comfortable lifting/ carrying -- not impossible, but really uncomfortable. Less would be great. More could be tolerated, if there was no lifting/ carrying involved.