I experimented with grapefruit seed extract years ago as a possible preservative for my wrinkle cream but found it to be pretty worthless. So I have not bothered with it since.
This is very interesting information you presented though and I looked in to it a little more and it appears that the claims are true. Here is more:
http://www.gaiaresearch.co.za/grapefruitseedextract.html
http://en.wikipedia.org/wiki/Grapefruit_seed_extract
http://www.naturalingredient.org/Articles/takeokagrapefruitseed.pdf
http://www.ncbi.nlm.nih.gov/pubmed/11453769
There are all sorts of natural antimicrobials including many essential oils. What is best would depend a lot on the application.