I like the web app... but a native iphone app will be even faster and powerfull

Think Gmail: it makes it easy to see all the "new" emails, which you haven't seen yet. It makes sure you don't miss an email, and that you don't need to read the same email twice.

Hahlo could do the same for tweets, with of course a more Twitter-like UI. Since Hahlo is server-side (not an app), it can fetch your tweets from Twitter are regular interval, and when you load Hahlo, it shows you all the stuff that has arrived in the meantime.

I'd like to have spell checking when writing new tweets. This would be a killer feature which none of the other Twitter applications are providing (at least on the iPhone).

Obviously, it would be implemented on the server-side, kind of like what Gmail does in their web interface.

when i post a new tweet and the page refreshes, instead of showing me the last tweet, it shows a copy of the first one in the list

I would suggest making hahlo.com work better from all manner of devices, not just those running webkit. The Blackberry Storm comes readily to mind. I'm not being selfish here or anything. No, wait. I am.

Instead of having just With Friends, Archives, Replies, and Profile, I'd like to be able to decide what my tabs are. This way I could have With Friends, Replies, Following, and Inbox, since I use those most.