It's a great tool, but I have one request: the slash line of the last tweet should ideally indicate how many total there were in the storm. For example, the friendly howto on your site should end with "6/6 Share and have fun. It's FREE!" This gives the individual tweet context when someone shares/quotes/screenshots it and it's being passed around: you know where the tweetstorm ends (instead of having to scroll down and look for a non-existent 7/ tweet).

Actually, since you're queuing up all the tweets to post them in one go, it should be feasible to add the out-of count to every tweet in the storm! That would be neat. But the last tweet should have it by convention.