For those who can't wait for 10.9 to get tabs, can't/won't upgrade to 10.9, or are using a paid 3rd party app (TotalFinder et al.), I found this little app a few days ago: XtraFinder (http://www.trankynam.com/xtrafinder/).
It works on 10.6+. It's totally free. It works great. It gives you tabs, and more.
Question is why the heck did I not find this before?