Store bought Kefir is supposed to be thicker - kinda like a yogurt smoothie. Store bought Kefir and store bought yogurt are very similar because they are both cultured milk products. I believe the store kefir may have a few more strains of beneficial bacteria, but that also depends on which kefir and yogurt you are comparing to each other. (some show the strains on the label so you can compare them)
Now home made kefir is an entirely different beast. It has LOTS of strains of beneficial bacteria and the consistency is more like soft curds and whey (I guess you could throw it in a blender to make it smooth, but I don't take that extra step :LOL).
I switched to home made kefir and add pureed fruit when I feel like being creative. The price at the store was $3 a pint and that's just crazy when I can make as much as I need for the price of organic milk. Also, this way I can make probiotic cream cheese, sour cream, and use it in recipes that call for either.
Here's a good website for kefir: http://users.chariot.net.au/~dna/kefirpage.html
and the nice thing is Dom's got all this info for you and he's not trying to sell you anything! Go figure!
Good luck and happy Kefiring!