I haven't previously denoted an anniversary date for WCF because there are so many to choose from. There's the date we were done, the date that downloads were available, the dates when various versions of Windows Vista came out that put WCF into public retail for the first time, and so on. The anniversary of the average of those potential anniversary dates comes to around today but that feels unexciting as a way to select the day. I kind of like using the first day of public downloads so that may be what I celebrate next year.
Last year I didn't need to worry about anniversary celebrations because we had just released Orcas at the one year mark. This year there has been no new release of WCF although we did get to deliver the mini-WCF in Silverlight 2.