While Google anounced the N5 and Android 4.4 it also revealed which devices are getting updates. Those will be the N4, N7 and N10. But not the Galaxy Nexus. Quite to some displease with Galaxy Nexus owners.
Good news first. You might not need to reflash your device. Bad news. You need to know what the hell you are doing to fix it. I recently stumbled into a nasty little problem and I'm apparently not the first and probably not the last. I wanted to update my CM10 nightly. After booting into clockworkmod recovery I had no access to any storage on the device. The apparently notorious E: cannot mount /sdcard problem. My first guess was a broken sdcard in the device as the external sdcard did cause some issues and in fact might have been broken.
A big problem and two simple solutions that cover most force-close problems with fresh cyanogen installations.
You have just upgraded your shiny phone to cyanogen and out of a sudden the new freedom is brutally stopped by force closing apps all over the phone. It is terribly annoying and it's mostly easy to fix. The somewhat obvious solution is to clear the caches and reset the phone. This however is a pretty drastic step and in many cases it's simply not required or it's not required and will not fix the problem.
Chrome 19 syncs tasks among registered devices. Required is - as usual - to register that device with your google account. I always failed to see why this is a specific handy feature. But since I'm using the beta of chrome mobile this is actually a pretty handy feature if you're leaving home or the office and want to continue reading within your tab chaos.
You just don't get 'open tabs' from another machine. You actually get a list of machines and their open tabs. So you can pull tabs specifically from various machines. IMO a much better feature than just sync'ing them.