My all-time favourite add from IBM is The HEIST. You might remember seeing it on TV or on the web when it was out in about 2001. The guy who thinks that all servers were stolen; he's completely het up, called the police and calls it "the crime of the century". When the police investigate the almost empty server room there comes another guy who clarifies the situation: all the data were moved to an IBM eServer running Linux - a small machine in some distant corner of the large empty server room. And the guy concludes that this move will "save us a bundle".
Looking at this clip again today even adds a couple of aspects to it. In particular, it illustrates the benefits of open source software with respect to energy efficiency and green responsibility. The clip correctly illustrates the efficiency of Linux running on IBM servers. You can reduce space both in terms of office space (for storing all the servers) and in terms of disk space; and you save money both for requiring less servers, by using open source software as an operating system, and by a reduction in the energy needed to run your server farm.
Everybody talks about green responsibility nowadays. One of the best ways to act responsibly and to achieve benefits for the environment is by increasing the efficiency of the systems and machines we use. The development model of open source software has the potential for developing better software which is more efficient and thus better in terms of it's environmental balance. Linux is a great example here. And it was all already there in 2001 ... in The HEIST.