TwitTruth definitely breaks down the honest Twitter usage of any account name. The homepage opens with a listing of the top 500 users and a breakdown of how they use Twitter. This is where the truth really shines.
The odds of getting a reply from many of them is very slim. There is a breakdown of the amount of replies, direct messages and my favorite column. The percentage amount of replies. Now all of these columns are sortable (it isn’t well marked, I just happened to click on the header). Martha Stewart was the worst (behind Twitter itself) which shows how a PR firm or staff might be working the account to get followers instead of the account owner. The top 25 or so for sure were all major celebrities or other known people.
I went ahead and listed myself and was stunned with the stats that it pulls using oAuth (with no spamming of your account which was great). It shows how often I tweet, how long to respond to directs, how often I mention a top 1000 user, how many times I reply, and it just goes on and on.