Wow, we've been doing treatments for the same amount of time! I actually started to get one in 2007 but I waited until 2009 to see how folk's hair responded to the treatment.
I never experienced any thinning or breakage but I did get permanently bone straight hair for QOD Max Orginal (it has over 3% formeldahyde). I couldn't even get bone straight hair with sodium hydroxide relaxers. Ironically, my hair was never, broken, thin, damaged or ragedy with keratin treatments. Relaxers couldn't stay on my hair long enough to straigthen my hair (due to my extremely sensitive scalp) but my hair was 10 x worse. I HATE relaxers.
Anyhoo, I started using QOD Max Organiq to keep my curls and doing root touchups works well! I don't think keratin is "temporary" either, well, it might be for some. I guess it depends on your texture, but like you when I do mine it's permanent.