This blurb sums up nicely the “concerns” over BioDiesel and your fuel system’s seals:
For something a bit more “scientific”, if slightly slated, check out the “Effect of biofuels on elastomers” section of this article:
http://www.dupontelastomers.com/apps/autofocus/a7/af7.asp?article=biofuel
In short, newer vehicles can usually cope, as they are built for biofuels, even if the manufacturer won’t warrant it. Older vehicles may have issues, depending on the types of seals they used. In virtually every case, however, you can (with relative ease, and less expense than you might think) replace older technology with newer (right down to the o-rings and seals in your diesel injection pumps).
Of course, there are other “issues” to Biodiesel use that one should be aware of (careful with the PH, watchful for contamination, you have find a place to dispose of your left-overs, such as the glycerin, the “final product” should really be washed, then de-watered, etc. This would be a great place to “mythbust”, or prove, those claims that it’s “just that easy”)
Here was the last time I remember this being discussed on Talk, along with a nice little video showing how easy it is…