Social networking done well is great right now. BUT....
I wouldn't hire "any" seo company. Most of them do NOT know what they are doing and can seriously damage your site's rankings. Google (the most important to rank in) has been going crazy changing algorythms and "what they want" from us and many sites that hired seo companies are dropping like flies after a fumigation. It's not like it used to be when a seo company could just spam links everywhere and rank.
There are some great SEO companies out there, but it's difficult for a business owner to know who to trust. Be cautious, ask exactly what methods they will be using, and verify results (if they say they acheive top rankings for a certain site and keyword, check to see if the keyword is actually competetive and if the rankings are CURRENT or from before the recent Google updates this month).
If you are interviewing a company right now, I would ask if they are familiar with the latest changes Google has made. They should begin to talk specifically about "the penguine update". If you feel comfortable with what they are saying and the methods they plan on using, then you can cautiously go forward. Check all of their work to make sure it's real and worthy of your site.
Sarah - from a real SEO and site development company.