Similar here. 15,000 miles sicne Jan. No serious problems.
Things maybe worth mentioning are:
1) Chipped the windscreen in May, which lead to a crack. Been waiting months for a large company that deals with windscreen replacements to get it sorted.
1st one failed QC the day it was due to be fitted.
2nd one was due in today but they didn't have a trim part they needed to complete the job.
Trouble is in between each cancellation is weeks of waiting for parts to arrive from Germany.
2) I don't like the charger cyling in the last 15 minutes of cabin preheat - as I've got a Rolec wall pod it clunks a lot. Sounds like someone kicking a ball against the wall. But if the charger was quiet it wouldn't be a problem.
3) The REX once failed to spin up to generation mode and stayed in warm up (low revving). Battery level dropped to 1 miles range. So I pulled over, shut down, restarted and all was fine. Well apart from it then revved it's nuts off till it got back to 6.5% SOC. Never happened since. I have a suspicion I pressed the REX start button (F8) literally at the exact same moment the car decided to start it up, and it caused it to think it was off in 1 part of the system and on in another. (Maybe, LOL).
4) Don't like the way ACC drops to regen mode when it gives up in awkward lighting situations (sun flare or fog etc). Should coast until you touch a pedal.
Other than that... I won't be swapping to another car unless it's a BEV with 200 miles real world range at 70mph and less than £40,000.
[edit jan 2016 - 23,000 miles.. the windscreen was finally replaced when I told my insurance company I wanted to use a local branch of a different national chain who I had contacted in advance to see if they could do the work. Book in on Monday replaced on a Thursday.
Cycling of the Rolecl was fixed in the i3 "Novermber update". Took it to BMW job done. However that did unleash a problem.. the HV batter was diconnected and when reconnected refused to charge. Everntually traced to a fault rocker in the charge port door release which the new software pays attention to as it has a warning if you leave it oipen when driving off.
Just stuck winter tyres on.. summer rears are nearly gone after 23,000 but enough left for a couple of thousand miles. Fronts looking good for 10k more.
Still wouldn't swap it for anything other than a Telsa at the moment.