I tend to use my real name online when possible. It's short, easy to type, and tends to reduce confusion. I'm not one of those people who thinks the internet is somehow less real than real life - if anything, I'd have a strong argument for the reverse.
Unfortunately 'Kim' is often taken, so I end up using one of my other standard usernames. I don't use them offline, though, and it confuses me when people do. It's more a login than an identity.
Like Kathy, my brain is hopeless at correlating names, usernames, faces and indeed bikes. So it all deteriorates into a best-guess muddle, with the quality of the guess depending on whether it incorporates a previously established online identity.