To me, it seems that companies such as Paizo and Mongoose do the best on keeping their release schedules. Of course, neither of those companies are 1 or 2-man operations.
On the other side of things, we have Eden Studios and Palladium Books, who sadly are leading vendors of vaporware and severely delayed titles. They aren't alone, but they quickly jump to mind as prime offenders.
As someone who grew up with Palladium Fantasy, I have been waiting for a new release for that line for years now. We were told repeatedly Mysteries of Magic was "coming soon", and to be fair, after a long, long, looooong wait, and seeing it on every press release for about five years, it came out. Agonizing as it is, and not to pick on Palladium, but after the 57th straight product was not released on time, why not start managing expectations?
Honestly, I understand. This is a hobby, and things get in the way. Lord knows they do for me. People are excited to share what they've written, I know. But perhaps, just perhaps, it's a good idea not to promise something until you can actually deliver on it.
The smart ones, I think, won't announce things until they're actually at the printer, or closer to it. Even then, you can have delays, but at least the product has been written and sent off to be printed.
How does your favorite RPG company do with keeping release dates?
Above: Was Vaporware For Better Part Of A Decade