Would a roll function for our excellent chat site help this site be a success? Would you use it?
I think having a chat bot that does it is sufficient. If I'm using it to game with a bunch of friends, I expect them to be honest. If I'm using it as a joke, or just to mess around, I don't really care about the fairness of it.
There is currently a chat bot in "The Game Table" chat room; however, it's kind of broken (try typing "8d6" in chat, and see what it produces. It would be nice to see it fixed, but I don't consider it a critical feature of the site.
I think there are plenty of options for folks out there that need dice rollers. I don't think I'd like to see this feature here.
Since the reported death of Google Wave, my group has been looking for a replacement for play-by-post. We might end up hosting Wave in a Box somewhere, but certainly I would consider running games on the RPG Stack Exchange chat. Keeping it PG might be a challenge, though, since my games tend to delve into "violence, horror and adult themes."
The Dice Service bot in the Game Table would meet my needs, but whether the community would actually want me creating a chat room (or two) for my own play-by-post game is a separate issue.