Pretty sweet. What kind of testing are you looking for? My first impressions, which are probably no surprise to you:
It takes a couple rings for the button to pop up, and I guess the camera button doesn't really work until the button pops up. Obviously it would be better if one or both were instant (or nearly-so), though I can imagine the difficulties with that. It seems like half the time it takes a few rings to answer with the slider, so I can totally live with the delay if necessary.
However, there were a couple times when the Accept button never did pop up. Which isn't a showstopper since I can always just slide-to-answer instead.
Do you think you'll eventually be able to add a button to decline? The back, then slide-to-decline is perfectly workable if that's not possible. You might also think about adding some camera button customization to allow a decline. Maybe a long-press of the first stage of the camera button? That would seem to be different enough from the short-press of the second stage that currently answers.
I was quite pleased that the camera button stuff worked for me. I have Button Shortcuts set up to toggle the brightness on my Droid, and I was worried that when I hit camera button to answer or to cancel the touchscreen lock, I'd be toggling brightness instead. Don't know how much of that is Android event handling versus your programming... but very nice to know I can still use Button Shortcuts at all other times.
One note about that though -- the way you have the menu set up currently, I thought I'd be able to use the camera button without the Accept button showing up (which would be nice to avoid pocket answering), but that didn't seem to work. So ideally I'd be able to answer using the camera button even without the Accept button showing up. But until/unless you're able to make that work, I guess you should make it so you can't check the camera button box if the Accept button box is unchecked.
I'm also wondering about the touchscreen lock. Any way to provide an additional option to make it come on as soon as the phone is answered? The way it is now, it seems like there's still potential for accidental hangup if the proximity sensor never activates.