Thought I'd update this thread, seeing that my Apple watch was delivered a couple of days ago.

I wore it with my phone in my back pocket and it pretty much mirrored my Sigma ROX 6.0 on distance, heart rate and calories. So it was pretty accurate there.

However, without the phone close by, even though it mirrored my heart rate correctly, it was really light on the calories, like after a 30min pace of avg 20mph and final 30mph sprint, where my heart rate was avg was in the upper 160's and 190's on the sprint. After 10miles it said i'd only burnt 250 calories.... Which was almost half of what I'd really done, and half of what the exact same ride at the same pace it worked out for me the prior day. So without the phone's GPS, it really is guessing.

So if you're someone who really enjoys the stats, then really you do need to keep the phone on you as well as the watch. Which is a little cumbersome for some.

There are some videos out on youtube showing the watch being used in a swimming pool, with no ill effects, so its probably more waterproof than Apple are letting on... (something to market on their next version, would be my guess)

But other than that, its a fun enough gadget. Very light and doesn't get in the way.