Sure, we'd all love to watch Flash-based videos on the iPhone, but until Apple actually implements Flash in MobileSafari, everything but YouTube (with its builtin player) is off limits. Or is it? Check out this little trick, in which you can use the "Download for Video iPod" option on Google video to watch almost any video instantly.
Now, my guess is that this trick presupposes a few things, first of all that you have a network connection from the iPhone that can stream video instantly. Also, I'm not quite sure where the video itself gets stored-- is there a temp directory in MobileSafari that would store this stuff? I doubt that the video itself would get added to your iPhone's videos library, but that may be the case.
At any rate, if you've got the connection (and maybe the space) for it, this is an easy, no-jailbreak way to watch any Google videos (or any other iPod-formatted web videos, I'd guess) that offer themselves up for download.