Not all tweeter clients are nice
Richard Stiennon has a nice writeup on TweetTornado. It started with a previous post where Stiennon detailed how TweetTornado may be damaging for tweeter. Judging by this last post it seems the TweetTornado guy is quite the asshole which may indicate that those features in TweetTornado were not really accidental.
I think one of the largest weaknesses of Twitter is the fact that the open API and easy interconnectivity between all users makes it easier for spammers to write clients that ‘cheat’ the system, while its reliance on a single infrastructure will make it easy for someone to take it down or make it practically unusuable for everyone. Look at Orkut, for example.