Was screwing around on the 'net and found a website you might want to take a look at. Most of the products that have been discussed here and at THT are probably safe, but check out this website. It appears to be a good source of unbiased info, since the only thing they sell is fuel tester kits. It did say that any additive with an "alcohol" in it should be avoided like the plague since these attract water. Users for SEAFOAM should take a look.
www.fuel-testers.com
www.fuel-testers.com