I think if you could make it just like twitterfox that would be perfect.
For example:
- New tweets could be highlighted;
- The Timeline window could be sizeable;
- When I right-click on a line, there could be the option to go to the tweeter profile opening the browser;
- The @tweeter and urls could be clickable and with a blue underline.
Well, along with juanico's ideas I guess that's all... for now.
If I remeber anything else I'll suggest here.
Thanks!