I stumbled on an old thread in the forums today in PC Games titled 'longest delay/s from a game?'
The thread ended (pretty much) in July of '07 with most of the posters agreeing that Duke Nukem Forever (or DNF) is the King-Daddy of lateness, and Spore should be in their somewhere at a close second.
Mind you, the thread is almost a year old, and even so, I am happy to dispell the notion on Spore being really late; it is only behind a couple years now. Spore has a couple to go before it is half-as-late as DNF (let us all hope it never gets close). Additionally, I wanted to take time to note that Duke is not the champ (EVEN ONE YEAR AGO vs TODAY!!!). But, the sad reality is that 3D-Realms, the creators of DNF, is the record holding developer (very very sadly).
It is true that Duke Nukem Forever is on track for the longest delay, but it was not the champ last year, and is not the current title holder. If you are old-ish, then you might remeber this, because even I was a twenty-something when this should have come out....
The longest-ever delay for a video game to go from announcment to release
...on any platform is...

11.5 YEARS!!!
(see Prey - Feb 1995 to July 2006)
Prey was supposed to come out right around the time of Unreal; I am talking about UNREAL, the first version, not UT or any other version. Both Prey and Unreal were in dev at the time, and though Epic took 3 years to unleash Unreal, Prey continued to remain in dev. Prey was 'in development' for 11 years from it's first announcement in Feb '95, until it's gold cd was minted June 28th, 2006; release followed on July 11, 2006.
Duke Nuk'em will most likely break the records, as it has been in dev since it's announcement on April 28th, 1997. So, we are mere months from breaking the record!!! Wired magazine readers have predicted Duke would do this since 2000 when they 'honored' DNF with the first of many Vaporware acheivement awards. Wired on order to make things interesting, went so far as creating a Vaporware Lifetime Achievement Award exclusively for DNF, awarding it in 2003 to the get the title off the list. However (and this is the best part), when they found it missing from the 2004 awards listings, readers overwhelmingly voted it back in and Forever won first place in 2005, 2006 and 2007. If Duke is not out by the end of Dec 2008, I am almost certain it will win again.
For the record (pun)...DNF will break the record on/about October 27th, 2008. GO FOR IT 3D-Realms, your reputation is riding on it !!!
Cheers from your local game historian,
RaQin
msudude211