First - I am very pleased with my powertap(s). I have owned 3 hubs: SL+ 24h (sold), SL+ 20h, Elite+ 20h.
I have owned an LYC, and 2x Joule 2.0s.
I am quite happy with my decision to switch from SRM to a powertap and have only had a few issues.
1> The last time I checked the LYC suffers from time dilation - reported here: http://forum.slowtwitch.com/gforum.cgi?post=2969032
As far as I know, still not resolved.
2a> My original Joule 2.0 had the interval button go bad after about 3 months of use, the second Joule 2.0 is now almost 2 years old and the mode button/joystick are starting to become a little finicky. IMO - those buttons should have a lot longer life then that!
2b> I semi-regularly experience data corruption on my Joule 2.0, that requires me to run chkdsk on it. I have an athlete (Mac user), that has this occur more often then not and is constantly calling for support to fix it.
3> At both Kona 2011 and Kona 2012, my Joule 2.0 experienced cut outs around Mauna Kea resort, just prior to the turn off the Queen K. In 2011, I figured it was due to low batteries, but in 2012 I put fresh batteries in - still an issue. Maybe everybody using wireless got nailed there though....literally the only place I've *ever* had issues; not even in my basement 5 feet away from my TV, stereo, computer, and two giant fans. That's the only complaints I've got about ~3 years of powertap usage. If I hadn't just acquired a Garmin 910XT, I'd be buying a Joule GPS - maybe in a few months.