i wondered the same thing. here's what i see at mae-east being
announed by some (i filter):
deny ip 10.0.0.0 0.255.255.255 255.0.0.0 0.255.255.255 (227 matches)
deny ip 192.0.0.0 0.0.0.255 255.255.255.0 0.0.0.255 (603 matches)
deny ip 198.32.146.0 0.0.0.255 255.255.255.0 0.0.0.255 (543 matches)
deny ip 198.32.176.0 0.0.0.255 255.255.255.0 0.0.0.255 (10 matches)
deny ip 192.157.69.0 0.0.0.255 255.255.255.0 0.0.0.255 (96 matches)
deny ip 198.32.128.0 0.0.0.255 255.255.255.0 0.0.0.255 (335 matches)
ya, ya, teh last four aren't rfc1918 but i filter them anyway (nap
dmz's) 
lot's of people announcing them. the first two are the
only rfc1918 nets i see announced on our nap routers.
-brett