It's an online account you can use to make your phone ring in your house to find it, locate it via gps anywhere, lock it and forward calls to a new number that people who find your phone can call, full phone and sd card wipe, I think it also has a full sync option to save everything but so far even the HTC sync doesn't work for anything but pictures and music with our phone. There are a few other things but you can look it up on htcsense.com. As far as I heard Verizon has exclusive rights to the Incredible 2 and that's why there's S support only but that's just what I heard from a Verizon exec that I know... we'll see I guess. ESET has a program in beta now that does some of the same things but you need to factory reset your phone to make them an admin so I didn't try it.
I believe it also has some customization features like more themes, skins, widgets, wallpapers. I may be wrong on that but I'm pretty sure it does.