Keeping URIs so that they will still be around in 2, 20 or 200 or even 2000 years is clearly not as simple as it sounds. However, all over the Web, webmasters are making decisions which will make it really difficult for themselves in the future. Often, this is because they are using tools whose task is seen as to present the best site in the moment, and no one has evaluated what will happen to the links when things change.
The message here is, however, that many, many things can change and your URIs can and should stay the same. They only can if you think about how you design them.
Cool URIs Don’t Change