I've become your typical Apple fan-boy over the past 3 years (prior to which I was a classic Apple-hater). I now own a Macbook Pro, iPad, iPhone and love them all. Having said that, as I buy more devices, synchronization problems between them are becoming more common and annoying.
Example : I get a GMail notification on my iPhone. I see it, clear it and check the email - awesome. When I get home and open my iPad, I see the same GMail notification that I already acknowledged and acted on - less awesome.
There's been a lot of conversation lately on how Apple's iCloud sucks for developers. As a user, I'd say it's even worse - notification synchronization is just the tip of the iceberg. With Dropbox, I don't have to think about synchronization because it's just works ("just works" used to be Apple's claim to fame no?). With iCloud, I have no idea what's being synched, if it's being synched and where to access the synchronized items (check out icloud.com if you want to laugh).
When iOS was made, it was the easiest OS to use. As we transition to a cloud-centric workflow, the "pre-cloud" (not fully but largely) world that iOS was originally developed is starting to detract from its ease.
Apple has a lot of catching up to do.
Update (6/29/2013) :
I just watched the iOS7 presentation from WWDC and saw that this was fixed. Good stuff Apple!