We buy our passes via 407-wdisney so that they are on our room key. By doing this I don't have to worry about forgetting them. Also if we lose one it can be replaced because it is on our "key to the world" card. Prices just went up in Aug. they should not be going up again for a few months.
Wait till near time to go in case a code comes out and you want to change to a packgage using a code to save money. you can add them to your room card any time or buy them at AAA etc. but deffinately wait.
I personally buy them early. My last trip I bought them early and the prices went up less than a week after I purchased. I ususally just go to a Disney store at the mall to get the tickets. Buying the park tickets before the trip is always exciting for me!
We have 5 in our family. Since there is no group discount for that many I started purchasing mine one a month once a month so that I could pay for them in cash.
We bought our tickets with Disney Visa online through disneyworld.com. We get a $40 credit on next months statements for using the disney visa at disneyworld.com, so I see that as a savings on our tickets. It ended up being a better buy than some of the ticket resellers (the good ones, anyways). We received them in about 10 days.