My major dislike in all that Adobe AIR stuff is that it looks all the same. For me, form follows function. Thus, I use Echofon for Firefox (some reading) and TwitVim (most of my reading and writing). No registry entries (not even for uninstallation) are created, no useless GUI blingbling is contained, they don't eat too much RAM and they don't require any runtimes.
You see? - Of course every AV program has some signature failures at times, but after all avast was disappointing. Of course it might be just my personal experience.
I switched from avast! to NOD32 about a year ago, disappointed by its detection rate, its awful GUI and its false positives. I really doubt they fixed it all in v5.