It is getting a bit ridiculous...but then again, Valve never set a release date, so really, we can't fault them. They have not broken the promise that they...never made.
I know it's funny to compare it to Duke Nukem Forever, but the comparison doesn't really work. Ep 3 is a game in the mid of its series, while the series has active releases, is a very successful and stable companies flagship IP, is sticking with the same engine, and has throngs of optimistic fans. Duke had none of these. My prediction is that Ep 3 will be released either at the same time, or within a quarter, of Portal 2.