Break out the birthday candles! Sing choruses of Happy Birthday! (Actually hold off on that, it might violate some license restriction somewhere.) But do celebrate! November 7th marks the 4 year anniversary of the launch of Tablet PCs. Lora Heiny reminds us that we now have 18 Tablet PC models and 4 Ultra-Mobile PC models as the Tablet PC turns four. Hmmm? Wonder how many we will see in year five? In any regard, say Happy Birthday to your Tablet PC today!