I am planning to record double sound using a high bit rate (320kbps) MP3 format with a Tascam DR-100. I like the size of MP3 files. I could fit an entire week of production on a single 16GB SDHC card and that would greatly facilitate files management. Is there any drawback in using MP3 vs. WAV in audible sound quality for interviews and ambient sound?

Yes...it's just not worth using lossy compressed audio formats like mp3 when wav files take up so little space compared with video.
The only reason all these compressed audio and video formats exist is because of disk space limitations. That's becoming much less of an issue now hard-drives and portable storage is now so cheap.
David

PostFade (http://www.postfade.co.uk)

I am planning to record double sound using a high bit rate (320kbps) MP3 format with a Tascam DR-100. I like the size of MP3 files. I could fit an entire week of production on a single 16GB SDHC card and that would greatly facilitate files management. Is there any drawback in using MP3 vs. WAV in audible sound quality for interviews and ambient sound?

Yes, because MP3's suck bad in general and even worse for production work (any editing at all). Definitely a VERY BAD IDEA.

My opinion is that I will allow my music bed to be an MP3, since most of what i do has VO covering the music.
But I would definitely have all of my acquisition be as high quality as possible. Uncompressed WAVs is the only way to go, I'd say.