I've got a couple weeks of use on my iBike + CP. Overall, I'm pretty happy, though there are some issues. Here are some answers to some of the questions, based on my experience:
Data accuracy: I don't have another PM on my bike to compare to, but I've tried comparing the numbers I get from iBike on a few climbs with those from analyticcycling.com, and they generally match up pretty well, within 5%. So, at least on climbs, it seems pretty good. I can't say for flats, but it "feels right" based on RPE.
Data cutouts: My experience, based on the roads I ride, is that the power reading cuts out about 2 to 5% of the time, usually for only a few seconds as I go across some cracked pavement, but occasionally for a while. It helps if your roads are low trafficed enough that you can chose the cleanest section of the lane. Higher speed = more cutouts as well. I rode a brand new chip-seal road, so new I almost slid out on the loose gravel, and the iBike cut out entirely. Older chip-seal roads vary, sometimes OK for 90% of the time, sometimes only 50%.
Inflated power numbers: yep this happens, but it's a small portion of the ride (1% or less, IME) and you know it when it's happening. The numbers aren't slightly high, they're ridiculously high, like 700+ watts. Since they're easy to identify in CP, I just edit the data with my best estimate as to what the real number was. Kind of a pain, but it would be much worse if, say, the numbers were off only a small amount and you never knew if they were right or not. The surest way to get a bad reading is to ride a fast downhill that isn't quite rough enough to cut the power reading out completely. The vibrations mess with the iBike's ability to read inclination, so it thinks you're doing 40mph on a flat rather than a 10% downhill and puts up ridiculous wattage numbers. Before correction, these spikes can really screw up the IF of a ride, as throwing even a couple 800 watt sprints into the middle of a FT workout really skews CP's calculations.
Power response lag: the iBike's response to power changes is damped. It seems to have a half-life of about 1 second, so if you jump from 200 to 400 watts, the display will read 200, 300, 350, 375, 390, 400, taking about 5 seconds before stabilizing on the new value. The same is true with drops in power.
Software issues: before the latest firmware (1.07), a lot of people had problems downloading their data, but that seems to be resolved by and large now. I had some issues, and John Hamann and Richard Wharton were excellent in helping me work them out.
To answer frenchy's question, the iBike App does a linear interpelation of missing data when it downloads the file from the unit. Assuming that the cutout wasn't too long and the before and after readings were reliable, that's usually OK. But if that's not the case ... more fiddling with the raw data in CP.
You can certainly make the iBike look bad by riding a lot of rough downhills. If you saw the two iBike/PT comparison files posted on the wattage list, in one, it did well, but in the second, the rider set out to torture-test the iBike and, sure enough, the NP and IF numbers from the iBike were substantially higher than the PT. But if you looked at the charts from that second ride, you could see that, even there, the iBike was reliable for 90% of the time, then went bonkers for 10%. Since that 10% included things like 5 minutes over 900 watts (on what appeared to be a descent, since PT was showing 0 watts for most of it), the IF was blown way up. In my normal rides, the bad sections are around 1%.
A couple of concerns that I've found which I haven't seen mentioned anywhere:
1) NO LAP BUTTON. The iBike uses "sub-trips" instead, which require you to hold a button down for 2 seconds to start and stop them. Hold a button down on a bouncy handlebar at the end of a VO2Max interval? Nuh-uh! Nor can you time yourself on hill repeats.
2) NO SCREEN THAT SHOWS BOTH POWER AND ELAPSED TIME. How the heck are you supposed to do a timed interval without that? The iBike people have a special-purpose interval tool that's supposed to be coming to the iBike app soon, but it's not there yet, and I'd rather time my own intervals anyway.
Hope this is useful to someone considering the iBike. Reading this forum is what got me interested in power training in the first place, so I thought I'd post something back in thanks.