If you use an AOSP ROM like Eris Lightning Bolt or KaosFroyo or CyanogenEris, you will not have the arc lockscreen to answer.
You also won't have, however, the beautiful SenseUI Home, the SenseUI widgets, the ordinary goodies that come with the Sense lockscreen, and a lot of the basic system features you come to expect in Sense that (some of which are enabled via CyanogenMod or otherwise) aren't all there.
It also is slow to ring, just like with Sense. But it is a completely different approach.
I also put my phone in my pockets upside down (since when I grab it and put it to my face, it's right side up anyway) and I've
N E V E R
accidentally answered my phone when putting it in my pocket that way. Top down. It's the way to go. 100%.
Plus it's easy to hit 'end' or 'call' right from your pocket when you need to hit it really fast.