[katastic]

Look at reddit.

    reddit.com/r/subreddit

    reddit.com/user/my_user_name   (Why not u? I don't know.)

Pretty straight forward. There are also ones like subreddit statistics and they're all... after the name.

    reddit.com/r/subreddit/about/traffic

(Note: Public viewable stats are only turned on if the mods turn it on.)

[edit] Wait. Reddit removed user access site-wide to those pages? Morons. Well, the URL point still stands.

[theoctopus]

Oddly

  reddit.com/u/foo

does work, but it just redirects to

  reddit.com/user/foo