If you want to read a very long (and slightly depressing) article explaining what plantar fasciitis is, and exercises designed to avoid/cure it, have a look at http://www.pponline.co.uk/encyc/0180.htm.
Other than that, I can't really help you with getting rid of it. My only experience of it is that for the past few weeks I have had discomfort in my foot that seems to match the symptons of plantar fasciitis, although it isn't bad enough to stop me running or affect my pace. It seems to have been caused by doing a fast 5k in thin racing shoes. I have found that it virtually disappears if I don't run for a day, and is only brought back by doing a long run. It seems to come back at about 10 miles as a discomfort which doesn't get any worse, but causes pain after the run. My plan (not entirely consistent with the advice given in the article) is to run as much as I can for the next few weeks without making it worse, and then give it a rest for a few weeks after the New Forest Marathon (22nd September).
Personally, I would be very cautious about having injections, unless someone could persuade me: (i) it was absolutely necessary; and (ii) it was going to do more good than rest or exercises.
If you have not done so, you also need to give some thought to what is causing it. Otherwise you might cure it, and have it come back as soon as you start upping your mileage again.