The personal one or whatever... but when I added my school's exchange OWA address I got an e-mail for the work version too

Battery impact is quite minimal... though present. If you're still using the stock Sprint radio, reflash it to the Telus radio, add Seven, and you'll -still- get better battery life

Edit: I've been using Seven for quite some time now. I absolutely love it. I don't know how I could deal without it, and I don't even use my e-mail all that much. It's just so nice to have the messages pushed to my device even before my PC picks it up most of the time. It also tracks read/not read and deleted status across the multiple e-mail clients. I have it set up for Exchange (via OWA... suck on that MCC IT department, who says I couldn't access my exchange stuff remotely), gmail, and windows live mail. This is definitely a program I would pay for.