I've only read up to volume 6 of 20th Century Boys... With all of the other titles I'm collecting, it sort of took a backseat to other series.
The English-language release by Viz Media is currently up to volume 18 but should be finished by December with volume 2 of 21st Century Boys (hmm, December 2012, quite fitting, don't you think???
) Assuming the End doesn't occur by then, I'll probably wait until I collect the whole series before resuming with volume 7. I've seen the first live-action movie and it follows the manga pretty closely.
(I just realized, what's scary is the fact that even after a year-and-a-half since I posted that list, I
still have about 200 unread volumes!
)