I've seen this somewhere else, but I couldn't find it again, so here it is.
Automatically download all RTMP stuff that flash tries to play (the second command *must* be run by a user different from the one you use for browsing or the auto-download won't work):
# iptables -t nat -A OUTPUT -p tcp --dport 1935 -j REDIRECT -m owner --uid-owner=<username or UID you use for browsing>
Videos will be downloaded into the current folder.
On Debian, rtmpsrv is included in the rtmpdump package.