[ericsoderstrom]

These problems aren't unique to tags, they're already present in subreddits names. For the most part it doesn't seem to be a big deal. As long as you can see the number of subscribers to a certain tag when creating your post, stackexchange style, then you'll probably end up with the tags you intended most of the time.

[toper-centage]

Exactly. You just need to take a look at www.reddit.com/r/subredditsashastags