Their limit is twice their number of users/tokens at the time of the official announcement, since they had more than 100k users at that time. They'll hit it eventually, but it'll probably take some time.
Their OS X client only goes up to 100k, I imagine, though.
> These tokens dictate how many users Tweetbot for Mac can have. The app’s limit is separate from, but much smaller than, the limit for Tweetbot for iOS. Once we use up the tokens granted to us by Twitter, we will no longer be able to sell the app to new users.
They were also forced to change the orientation of your own tweets (they used to be on the right), and to change the way tweets are displayed in the full view. Notably, they didn't comply with the rule that says that all tweets must have the twitter logo present somewhere on them. Hopefully that one doesn't come back to bite them.