I always think that I'm going to regret having sold a bike or miss it - but truthfully, I've never ended up regretting it - because usually I'm selling them because they didn't quite fit or weren't right for me and because I've got a replacement that is better. About 3 of my current bikes are perfect for me - and if I ever had to sell them for money, yes, I'd be really upset about having to sell them.

I vaguely regret that my childhood 10 speed isn't still around so that I can make a singlespeed out of it, but...