Guess I'm a lucky one
I live in the Dallas, TX area and so far I haven't had any problems with my internet connection (my IP address even stayed the same). The traceroute does show it taking a path through the Frontier network now, so maybe they've only changed things a few hops upstream. However, I have heard a few people in the same general area that have been having problems (e.g. someone paying for 75/75 service and now only getting like 16/12 on a speedtest). I tested mine last night and was still getting the 50/50 service to which I'm subscribed. They did break reverse DNS though (at least for my IP address), which can cause delays on SSH connections that try to perform reverse DNS lookups (i.e. the default config).
My biggest worry is if/when they are going to start implementing "Copy Once" DRM on the channel lineup. Verizon only use "Copy Once" DRM for premium channels (along with some Fox channels starting last year), and "Copy Freely" for everything else. From what I've read, Frontier typically encrypts everything but local OTA channels. I have a CableCard with an HDHomerun and MythTV, and if they start doing that, it practically becomes useless and I'd have to resort to WMC (ewww).
I generally haven't have any problems with Verizon over the years except for the occasional billing snafu when I make plan changes or some idiots cutting a cable outside.