Other than mass-mailing bloggers and submitting to twitter directories, what have you done to bring traffic to your site?
That's been about the limit of it - attempting to get relevant users visiting the site, as there's no point in getting millions of visitors who have no interest in Twitter tools :-)
Also, I'm interested to know unique visitors vs. free users vs. paid users, as I'm sure many others here are wondering as well.
Hrm, I'll have a think about that and maybe write a small post about it :)
Also, how have you handled existing customers when experimenting with price changes?
Probably the wrong way. Customers stay on the plan they're on, so the lucky subscribers who are on $20/year stay on $20/year until they cancel their subscription.
I had two customers complain when they were paying $9.99/month and they say the new $19.99/year price. I explained that I was experimenting with pricing, that it was likely to change in future, but if it didn't then I'd be happy to offer them the new rate. It turns out that they've also done well now, so I think in the end everyone's happy :)