I have seen a bunch of iPhone advocates bringing up the "seamless" nature of the iOS and OS X products and their overall superior quality.
While I agree in principle, I think the Apple ecosystem has some serious issues right now. Here are just a couple off the top of my head.
1. I always run into trouble because my Apple ID (which I've had since the .mac days) and my iTunes ID (which I got when the store opened) are different. The biggest issue is that whenever I upgrade to a new iOS device, somehow it always ends up using my Apple ID to try to access iTunes or something. When I try to get into my iTunes Match, it won't let me switch the IDs (says something about having to wait 90 days!?). I literally have to go through iTunes Support and have them give me a special dispensation to switch the accounts. Yes I think iOS did pop up some message about using one account or the other, but it's so ambiguously worded and unclear of its consequences, that I must somehow chose the wrong response.
I've had other issues with having two separate IDs, although I can't remember the details now. But I should be able to merge them! No dice.
2. I never thought I should have to pay for texting on my iPhone, so I've always blocked it and used a Google Voice number instead. With the advent of Messages/IMessage, I thought I could finally communicate more cleanly with my friends who use Apple stuff. But it's so wonky I have almost given up. If someone sends me a message, Apple to Apple, it should simultaneous pop up on my iPad, iPhone, and Macs. But no such luck. Most times it goes to one device. Sometimes it goes to some combination of two. Never does it go to all. I can't make rhyme or reason of it. This is supposed to be so simple and easy, why can't it just work?!
Also, most people know my Gmail address, not my iCloud address. I've tried adding the Gmail to OS X Messages, so that someone could send me messages that way. The application accepts the Gmail address and claims that it will be sending me a confirmation email to finish the setup. Confirmation emails have never arrived, and I gave up on it. I took Messages off my Dock because it's basically useless to me these days.
3. Somehow, between all my devices, I have 4 or 5 duplicate sets of web bookmarks. At least a couple times I went through and deleted the redundant ones, and they came back. That's just stupid.
4. I am still rocking the original iPad. I think it's funny how quickly it became ineligible for iOS updates, but the other part of me says thank God for that. It is so painful to just run iOS 5. Apps shut down All. The. Time. Safari browser hangs and crashes so much that relaunching it is engrained in my muscle memory and I don't even think about it. The fact that I still doggedly use this thing is a testiment to the greatness of the tablet form factor for lots of purposes, but man....if an Android geek ever saw the hurdles I jump through to use this thing, they'd have a field day. I imagine that most of the issue is probably the fact that Apple, in its infinite wisdom, decided 256 MB of RAM were enough for the first model.
5. I had an iPhone go bad on me unexpectedly (it got really hot in my hand and the screen got all rainbow ripple-y and then died, all in about 3 seconds). This happened at about the 1 year 2 month time, so just out of warranty. I went to the Apple Store and ended up paying $180 or something for a refurb replacement. I *KNOW* with certainty that I had set the dead iPhone to automatically back up to iCloud when it was charging and on wifi, and it had done so...for awhile. But when I got the new phone, I discovered that my latest backup was from 2 or 3 months earlier, even though I set my iPhone in a charging dock on my bedside table every night, and assumed it was doing its backups. Somehow, in some iOS point upgrade, that auto backup got turned off (I guarantee I never did it myself). So although I thought I was protected, turned out I lost some stuff (bunch of stupid unimportant photos but also a few videos I had shot that had a lot of sentimental value).