The widget box should be fluid, so it can fit into tiny or large spaces on a website and be more flexible to web designers. Allow custom width/height inputs and make the content in the widget adjust appropriately. This would improve it massively.
Also, allow users to select how many tweets they want displayed, whether or not they want display pictures to be seen, etc. All these small things really make it easy to integrate into other websites. There should be an option for no scrollbar, as there was previously.
You’ve allowed people to select an RGB value for the link colours. Why not do this for other aspects, e.g the non-link font colour? Or how about allowing RGB values for the background? The dark/light preset themes sure as hell aren’t going to fit in with most websites. Facebook has the same preset themes but they’ve allowed us to select our own colours in the actual markup though.
Also, users should be given the option to remove the “Tweet to @username” at the bottom. I find it quite annoying myself, and it’s also encouraging spam.
I know you guys are working on the customization and most of these probably won’t be possible, but I’m sure there are tons of people that would benefit from some of these features. The more customizable it is, the better.
I hope this was a bit constructive and I also hope that you’ll take some of these into account. This is the first time I’ve been on the dev site. Thanks for reading.