It was a very bumpy ride around 3.5-rc1, when even awesome's own libraries were slightly broken. And upon encountering any syntax errors in config script, awesome would kill the X session (very annoying when using some login manager - it was hard to find the reasons for errors). At some point i just switched to dwm.
Fortunately, things seem to have been resolved now. You just have to start from scratch with default configuration and use your favorite merge tool to re-apply your customizations. 3rd party plugins might require some rewrites, though.
And most of the time, config file with syntax errors will not prevent awesome from loading and showing a couple of popups with summary of errors. So if you mess up, you will know what is wrong. A welcome upgrade.