I'm going to quickly look at one of the longest lasting ad campaigns that is still running--Apple's series of "I'm A Mac" commercials.
One doesn't even need to see the product in order to get the representation. Justin Long's 20-something, nonchalant look suggests that it's cool to be associated with Macs. To the contrary, John Hodgman does an excellent job of portraying the dull suit who uses his PC in the office or somewhere equally bleak.
For roughly three years now, this has been Apple's primary television campaign (speaking in terms of computers, rather than iPods, iPhones, or accessories). Irrespective of new models or features, the representation doesn't change, and while there may be occasional cameos, each actor is associated with his respective brand. We can CHOOSE to be on the verge of something new and exciting (in this case, technology), or stick with that of a previous generation.
Several weeks ago, Apple released its newest batch of ads in this campaign, and I'm amazed at how relevant and fresh they still seem. Archived commercials are linked on their website--people actually want to watch them, rather than avoiding them, like most commercials.