Several people have switched from Twitter to Pownce, but I seem to be the only one who prefers Twitter.
Pownce has several features that Twitter lacks, such as sending files & links, and it doesn’t limit messages to 140 characters. Unfortunately Pownce is crippled by the lack of a public API and their desktop client just plain sucks.
I really hate Adobe AIR applications. I’d rather have a lightweight client like Twitterific that doesn’t require any runtime software. The only other option for Pownce is using the website, and keeping the page open all the time is less convenient than using a desktop client. Pownce’s desktop client has lots of annoyances aside from being written in AIR. It doesn’t log in automatically and there’s no way to keep it from displaying error messages which blur the window contents until you dismiss them. You also can’t reply directly from the client – it switches to the web browser for replies.
With Twitter, I can post updates via SMS or IM, and even automatically tweet when I post a blog item. Pownce offers no such options. I can also receive my twitter updates via SMS or IM, and twitter even has a mobile page that looks nice on an iPhone.
If anyone still needs a Pownce invite, I have 9 left.