QUOTE(D&N @ Dec 27 2007, 12:49 PM)

You are not here illegally if you have pending application. You're sort of in....a gray area. You can legally stay, but if you leave the country you won't be readmitted.
I am not a lawyer, so take my word for what it is - an opinion of an informed layperson:
You are not in a gray area - if you have filed in time, you remain a permanent resident, with or without NOA, until the USCIS adjucates your case. If people loose their NOA, they don't become illegal either. If you would have to leave the country without NOA on a short notice, e.g. for a funeral, you would be readmitted, but it would be a long and tedious processing at the border - by the way, when I reentered the US with my NOA, it was a long processing, too: they didn't trust the paper, but first had to find me in their database. In summary: After filing timely, you remain in legal status, but it is always good to have written proof of your status, which is the NOA.