What is it that makes this very web site so nice to use, where even wandering about is pleasing?
The voting. No really, hear me out...
On SO, all of the "thanks!" noise from the old-school forums and mail lists — and much of the flamewarring — is nicely condensed into a vote on the question or answer. The voting on answers also acts as a filter, most people know they can read the first one or two and skim the rest (makes "wandering about" nice). It also encourages decoupling of answers from each other ie. they are not replies in a discussion, which further quashes flamewars and focuses content. The reward of personal recognition attracts people who actually know what they're talking about. It also means that instead of organising information by time, it can be organised by... actual information content!
This all leads to a relatively high signal-to-noise ratio for the whole site. This, in turn, allows for a cleanness of presentation that is absolutely impossible on, say, a threaded email discussion or a forum with posts stapled together one after another.
Using time as the sole dimension for organisation restricts how a site can be presented and used. Voting adds another dimension, which means that strange new interface and design decisions are possible (and even suggest themselves).
