RePhresh is supposed to restore the slightly acidic Ph that your vagina likes to have in order to avoid yeast infections. I had a reoccurring infection over the summer- I think it was a combination of heat, bike racing, and stress. I decided to try the RePhresh (I had put it off since the stuff is expensive- ~$20 with tax for 4 doses), and I was very very happy with the results. I used it at the first twinges of an infection and it got rid of any itchiness almost instantly, and it didn't come back! The manufacturer says you can use it as often as every 4 days, but I found that I end up just keeping it around just in case I feel something coming on (I've only had to use it a couple of times in the past 3 months).
I say it's money well spent if you have any issues with yeast.