I know exactly what you mean about the oesbssion with letters .lol. My 3 1/2 year old son has been obsessed with number and letters since he was about 1 1/2 or so. It all started out with license plates too. You can guess how long of a trip it was going from the car into the grocery store at that time lol Wonderfully though this oesbssion has lead to early reading, which he's been sight reading for almost a year now, and recently started sounding out words. Thomas was diagnosed last April with Autism, and after a whole lot of therapy and mom helping we're doing a lot better.