We reviewed Tweetian recently, and found that while it was very good for a free application, it wasn't avaiable to Nokia Belle devices. Fortunately, the problems that were holding Tweetian back have now been overcome and it is available for all Symbian^3 (i.e. Anna and Belle) devices. The developer, Dickson, has also written on their blog about the download statistics of all of their apps. The Tweetian statistics brings out very interesting before and after picture that suggests the proportion of people who have not upgraded to Belle is a minority.
Before Tweetian is published for Belle (only published for Anna/pre-Anna), Tweetian already have cumulative downloads of 12,000+, and having 200-600 downloads per day
After Tweetian is published for Belle, Tweetian have a daily downloads of 1,500-1,900
If you don't want to buy a Twitter application, Tweetian is certainly worth a look.
In balance, Tweetian has far more features in its favour than there are complaints to make. Of course, the main drawback with Tweetian is that it is currently restricted to Symbian Anna devices, but that should be changing very soon.