Cappy's is a rarity on Walnut Street: it's as close to unpretentious as you'll ever get in this affluent and often snooty shopping district. As others have noted, it's a dive bar that happens to serve pretty decent food; my wife thinks that the Big Mountain sandwich is to die for (and I'd agree). The service has always been friendly, and it never seems to get as loud in here as it gets in some other places (Shady Grove, I'm looking at you).
I know it might sound strange, but one of the things that I appreciate the most about Cappy's is that it treats its waitresses as waitresses, not as sex symbols. I've always found the skimpy outfits that waitresses choose to wear (or are made to wear) at some other places to be rather insulting -- these women are there to do their job, not to be ogled at by everyone in the area. So thumbs up, Cappy's, for treating your female employees with some respect!
My wife and I moved away from the Shadyside area a few months ago. Cappy's is the one thing we miss. Big Mountain forever!