I stopped using toothpaste a few months ago when I ran out and noticed that brushing with plain water seemed to work just as well (by the feeling of cleanness when I rub my tongue over my teeth). I also drink a lot of tea, so I'm already exposed to quite a bit of fluoride and I'm more concerned about excess than lack of it. I am also somewhat suspicious of the long term effects of antibacterial agents present in most modern toothpastes.

BTW, if you want to search for scientific papers about toothpaste, the word to use is "dentifrice". One interesting study I found (free full text available):

http://www.ncbi.nlm.nih.gov/pubmed/20657090

"Dentifrice use does not enhance plaque removal when used in conjunction with a toothbrush, and instead, may marginally lessen the brushing effect. The role of a toothbrush appears to be more crucial in the maintenance of oral hygiene."