I had a MotoActv. It was a decent novelty once rooted (Angry Birds worked great as did a few other things). I had Honeycomb running on it. That being said, it was not good for battery life (no way in he.. it would last a long race, especially a marathon I'd assume). I'd say on normal use without GPS runs it may run 2-3 days on a charge. With activity, it diminished quickly. The step counter like most wrist wear-ables was not accurate. If you want it for that, get yourself a fitbit. I've found NOTHING that compared to fitbit (regular pedometers, phone apps, MotoActv, and Basis Band cannot compare). Also, and a big warning, unless you find a way to protect this thing with a skin of some sort, you're likely going to break the screen. I was fumbling putting my MotoActv on in the morning after a shower and it fell from waist height to the tile of my bathroom floor. It hit the corner and it shattered the screen because the glass is raised on the bezel. You've been warned. If you want a pic of mine just Google "cracked motoactv screen" and it will be the first result. It's like $70+ shipping to get it replaced. I ended up selling mine to someone that had a good screen but bad circuitry or something in his. I currently use a combo of Fitbit One, Nike+GPS watch, and on occasion my Basis B1.
If any watch designers are out there reading this, this is what you need to make for a REAL fitness watch:
Design it physically similar to the Nike+GPS: double-wide clamp down strap (to keep strap from breaking and to keep it from flopping around on the tail of it), Eink screen (yes color is fun and exciting, but it sucks in daylight and it kills your battery - neither of which is good for running/fitness outdoors), backlight that is bright.
Also from the backlight option a hybrid of Nike+GPS and Basis. Basis uses the accelerometer to know when you turn your wrist in the direction to look at your watch and comes on, Nike+GPS allows you to flick your wrist or tap the screen to enable it. All 3 of these combined would be perfect.
Get the sensors like the Basis B1: galvanic response, skin temp, and light based HRM (no chest strap needed).
3d accelerometer, but find a way to make it as accurate is the Fitbit One. I hear the Fitbit Flex is actually quite good, but I can't speak to that. All I know is every wrist based one I've seen or tried hasn't, but if you can figure that out, kudos.
GPS. It must have GPS! I'd like to have this as an open standard like GPX and then it could sync to any number of sites. Also, if whatever "portal" or "software" is used with it could find a way to sync or at least import from the TCX files from Nike+'s site, that's a bonus because I have a ton of history there. I really hate that they have a proprietary format, but I love their hardware, so it has been my primary.
Track multiple sports! This is the other downside of Nike+'s hardware/software. TomTom branched off from Nike on their own and came up with some good watches, one of which is a multisport, so they're getting there, but they require a bluetooth chest strap for HRM (I HATE chest straps!!!) and I don't believe theirs does accelerometer/pedometer/stairs tracking. They kept with a similar design of the Nike watch and so they've almost got what I want aside from accelerometer and sensors like Basis.
Bonus points too if they make it bluetooth compatible if people do want chest straps, to use bluetooth headphones for hearing your pace etc, to sync to phone wirelessly, and also to have an API that it could control apps (like Pebble does). To be honest though, the API would be the last on my list, because I never trust phone batteries to withstand long runs. Hey, I'm slow! It's yogging.
Ok, so in a nutshell, use the MotoActv for hacking/AngryBirds/music and not fitness, be careful not to drop it, and get a TomTom MultiSport, TomTom Run, or Nike+GPS watch and a Fitbit One if you are really intersted in tracking fitness.