Droid allready does sense UI. Eris is only a nock off of the hero lol, Dont get me wrong good little phone but not in droids league sorry.
Normally I don't feed trolls, but no one would argue that the Eris is more powerful or more capable than the Droid. It simply isn't true, the Droid is a beast and has tons of power. However, I, along with many others, bought the Eris for a few reasons.
1) True Sense UI supported by HTC and upkept by all updates.
2) cheaper price
3) form factor, nice and small, feels good in the hands
4) NOT the ugliest phone ever made. Seriously, the droid is the product of a 15 year old who was told "design a manly phone, don't worry if it's ugly, it just has to be manly".
5) no physical keyboard, they're a waste of space and add unneeded bulk to the phone.
6) trackball, it's great for games and using the phone one-handed in the car and serves as a cool silent notification.
I knew the Droid was much more powerful and yet I never even considered buying one. And yes, I had more than enough money to buy one. If the Nexus One would have been available, I would have bought that. It also has some of the same advantages as the Eris, specifically numbers 3, 4, 5, and 6.