It is true that Snopes.com is run by a husband and wife team. That in and of itself does not mean that the information they present is not accurate. I've seen the e-mail you referred to, stating that the information they present is slanted to the left. I think the primary reason is that the majority of the political e-mails they check on tend to come from conservative writers. Certainly, I receive far more e-mails that might be termed conservative than liberal. Most of the liberal ones are jokes of one sort or another. But if you've looked at the site, political e-mails make up a small part of their fact-checking.
Here's what they authors have to say from their FAQ:
Q: Who creates the material for this site?
A: With very few exceptions, all of the material on this site is prepared by the same people who operate this site, Barbara and David Mikkelson.
Q: How do I know the information you've presented is accurate?
A: We don't expect anyone to accept us as the ultimate authority on any topic. Unlike the plethora of anonymous individuals who create and send the unsigned, unsourced e-mail messages that are forwarded all over the Internet, we show our work. The research materials we've used in the preparation of any particular page are listed in the bibliography displayed at the bottom of that page so that readers who wish to verify the validity of our information may check those sources for themselves.
When I receive something that I think might be inaccurate, I usually check Snopes first. If they don't have an entry, then FactCheck.org is usually my next stop.
EDIT: Here's a link to what FactCheck has to say about the Snopes e-mail:
http://www.factcheck.org/askfactcheck/is_snopescom_run_by_very_democratic_proprietors.html
