If you'll remember, judicial meanz, HipShot and myself had a conversation on this a few threads ago. I used US Border Patrol stats from the last ten years to show the potential for up to over 70,000 terrorists inside our country right now. Of course, not all of those will be "trigger pullers" some will be for intel and logistics, too.
Timing is everything, here. I have no idea how many of these preplanned operations will have been interdicted by our Intel and LEO guys. Other plans could have been disrupted by the heat. The extent to which contingency plans have been made in case of these types of ops by our guys is unknown. The Jihadis could have Plans A, B, C and D all lined up, or they may have no fallback plan beyond a I'm on my own mindset. That would be a good thing on the one hand in that the B-I-G bodycount plans may be off the table, but a B-A-D thing in trying to stop events on a smaller albeit still violent level.
By the definition of sleep cells being groups here hiding and plotting until given the go ahead I agree to that definition. What I think we saw on 911 is a group that laid low but had a definied mission that they worked towards until they felt they had a reasonable chance of a successful operation. That this operation lasted years may give the impression of a 'sleeper' cell, but not by a rigorous definition IMHO. By the more conventional definition of sleeper cell, the group in deep undercover for potentially decades before activation.
Sorry it took so long to reply to the thread. Been a trifle busy.
I've been following Tom Marzullo on his take about the sleeper cells and whats coming. He has a fascinating take. This is a link to some of his articles:
http://www.mensnewsdaily.com/cgi-bin/search.pl?Terms=tom+marzullo&Match=1&Realm=MND&submit=+Search+
This article is particularly enlightening:
http://mensnewsdaily.com/archive/m-n/marzullo/2004/marzullo072204.htm
I'm with you on the mindset. These guys have no clue of that they are facing.