I use pretty much all of the features that it lets you do but i think the one i use the most is the fact that i can be texting back and forth with someone, then when i get home on the computer, i can continue to send and recieve texts from the voice website.
got an EVO on launch day and it was a new sprint account for me so i setup "voice" on it and gave everyone my voice number. havn't given my "real" number out to anyone. now i have 1 number forever and i can change what phones it rings on to whatever combination i want.
it's really slick actually