The high volume of complaint forums happens with every software update on just about every device. That includes Moto, Samsung, LG, Apple, it doesn't matter. A huge part of what the forums are is a place for people with common issues to share resources for troubleshooting, so it's natural to see the bugs, etc detailed out.
The presence of a user or even several users with an issue doesn't address the ubiquity of a potential issue. Ultimately we're looking at a very tiny cross-section of mobile users when we restrict to those who use forums (easily less than 1-2%), and if 1-2% of those members are having issues it doesn't indicate that the issues are not real, just that we can't make assumptions about how widespread, how serious and how easy or difficult to work around they are.
Many forums are filled with posts by people who will make one post on several different forums about their device "issues" and never respond.
We do know that (and have explained why) some apps do not work as they did before with SD cards and have always recommended that people remove those cards prior to accepting or forcing an update. Aside from that one (which impacts everyone who updates and had apps that used the pre-JB app2SD method that haven't been updated for 4.4), I haven't seen many bugs that look like they're more than one off flash-growing pain items.