ZERO problems so far! I use everything daily alarms, calendar, all the integration with different apps with People hub and else... for gaming GTA, Fifa 14, Modern Combat... I use it for internet sharing, GPS, googling stuff, whatsapp'ing all day!
HEAVY USER! and NO problems! and battery last a day easily! by 6-7pm is around 40%, by 10pm is around 15-20% because at night I turn on the internet sharing and chat heavily!
maybe just little ones..
-games lagging after a while, only fix I have found is to restart the phone!
-and the music player, if you hit the shuffle button, it will shuffle but if you chose a song and hit the aleatory button it stills plays the music alphabetically!
-my phone is cramped with photos! in some apps, you can change, upload, send photos right? it starts loading the gallery and sometimes it closes after a few seconds!