Have you noticed an increase in your SQL filesize?
I updated to Nextgen 2.0 then rolled back to 1.9.13. Now I have an SQL filesize that is almost 200K larger than before.
I compared my former SQL save and the new one and there is a lot of new NextGEN code in the 2.0.0 version, even after downgrading to 1.9.13!
I am not an expert on this, but I can see that the filesize is bloated by NextGEN and now I cannot get rid of the extra lines that I don't need (I've changed the content of my website a tiny bit in the meanwhile, a simple SQL replacing won't help).
Mostly the "postmeta" and "post" tables increased. I haven't done any now posts...