No, suprisingly not. To be honest when I tried this out, I was just waiting for it to fail and not work. I thought that if I just dropped the ffmpegX created files into the DVD from iDVD there would have to be something that didn't fit or work. But it had no problems

I've tried it by making a DVD made of four episodes of a TV show, each about 40mins long and about 1gig in size. I was using one dummy file four times over. As long as I replaced all the files (VOB, IFO, BUP) for each of the episodes/dummy file and didn't touch the VIDEO_TS files it worked fine.

I guess there's nothing stopping you from messing about with the bitrates of your MPEGs you feed into ffmpegX to make a DVD thats longer than the default 180min. This is basically what apps like DVD2one and ffmpegX's DVD>DVD4GB tool does I assume?

Break out your Terminal.app!

You can grab the transcode source from http://www.transcoding.org and build it (the messy part)... there's a utility in there called tcrequant. Run it after you demux like so:

tcrequant -i videopart.m2v -o videopart.new.m2v -d2 -f 1.5

The 1.5 is the requantize value. 2.0 is roughly half size. Then you mux the new one back together with the audio...

...or you could just use another DVD.

This may be handy to squeeze some BIG movies on to one disc, though. Or you might just get it down to a simple batch process, since this suite does demuxing too.

I haven't tried the above on my Panther. I have done it on Linux though, and the quality remains very good, and the conversion speed is still definitely faster than reencoding. Downloading the source right now.

Don't know if this helps any...