They are amazing. A product like CQuartz UK will last 2 years and you can buy that online and do it yourself. The prep work is key as the paint has to be better than clean for the coating to stick. I did both our daily drivers last fall and they both still bead water better than any wax or sealant I've ever used and we live in a fairly rugged high elevation climate. CQuartz UK is the only ceramic coating I'm aware of that you can buy, for the more high end stuff you have to have take it to a detailer. I recently had my 997TT done with Opticoat Pro Plus which is guaranteed to last 7 years. The detailer had the car for 3 weeks, did a full paint correction and sealed everything, calipers, wheels, door jams etc...
http://www.carpro-us.com/coatings/
^These guys carry all the good stuff and they have a bunch of good how to vids on youtube.