We all have seen and remember the various versions of the Mac vs. PC ads. The ones that have the semi-overweight, nerdy, thirty-something year old "PC guy" and the likeable Jake Long as the "Mac guy"? Why are these ads so memorable? The combination of humor, distinct characters, and famous actors like Jake Long help us to recall these ads.
Getting people to remember advertisements is the first step in an effective advertisement campaign and these ads do a very good job of it (at least in my opinion). Also the humorous situations portrayed in the Mac vs. PC ads make people like the ads and, in turn, like the product.
The fact that people like and associate, with the Mac guy is a useful advertisement technique, as people extend the positive associations with the Mac guy to the actual Mac product.
Most of the commercials also have various inside jokes or jabs at PC's that highlight their "flaws"; such as one where the PC guy has to constantly pause to buffer.
The repeated use of the same characters and actors in Mac's ads helps to build viewers' attachment to the "Mac guy" and reinforce the positive stereotypes about Macs and the negative stereotypes about PCs.