It doesn't seem to bother him much, but it's much more noticeable than it was a few months ago.
Fortunately, he never has to jump more than eighteen inches or so; there's always a chair or stool for him to use. That's been true for years now, before he lost all that weight the vet warned me about making him overexert himself. Additionally, we live together in a shoebox, his food dish is near his hutch, near the couch, near the bedroom, near the catbox. I don't think he walks five hundred feet per day.
Still, it's a concerning sign of age. I'm going away for a while, and while the neighbor checking on him is very nice, I don't want to be away if he's starting to fail. I don't want to think about his mortality.