There should be a special place in hell for Web developers who disable your "back" button. I'm sure it's happened to you before. You're surfing a Web site, finishing copying down the recipe for garlic-pineapple pickles in aspic, and then attempt to return to the page you were looking at before the craving for garlic-pineapple pickles in aspic assailed you. No go...you're stuck.
What the Web developer is doing is not so much "disabling" your back button, but causing the same page to reload each time you try to go back. The result is: no matter how many times you click back, you're like a gerbil on a wheel. A lot of effort, but you're not going anywhere.
This is a particularly annoying trick in the Google era. Crafting a Google search has become an art: a mix of "exact phrases" and single words that generates a page that is of interest to you. We've honed our skills through years of using search engines, and can now lay money on the fact that we'll get a relevant hit to what we want every time we search, because we know the quirks and tricks of the search engine.
Problem is, when you follow a link off a Google results page, and then find you can't go back, you've lost your carefully crafted search and have to start over again.
The way I look at it, the kind of Webmasters who disable the back button to keep browsers on their sites are probably the same kind of people who think locking their dates up involuntarily in restraints will only result in helping a lovely evening go on for longer. The thought process is bewildering, to say the least.