Valve is rubbish at the whole "release content in a timely manner" category.

Regular episodes of HL2 were promised four years ago and since then we've had four hours of gameplay every 18 months.

I'm pretty sure they do it for hype reasons. Negative publicity such as "OMG it's delayed, I'm so frustrated" is better than no publicity, and it's virtually free.

No, it's being delayed to avoid being cannibalized by Gears of War 2 which was coming out on that same date. Thanks for going to consoles Valve, thanks for letting them decide PC game releases. Just what we needed.

maybe they're just spending too much time "playtesting" TF2.

No, I remember back in 2007 when the game was announced and they said that they anticipated an April release that year, a mere couple of months from the initial announcement. Anyone else recall that?

That was probably before the original mod team had been absorbed into Valve -- once they got absorbed, they saw the flawed perfection throughout the game and had to remake it 3 times over. ;)
EDIT: Whoops, supposed to be a reply to #4.

Christ, I have plenty of stuff to play this fall, but this one I was especially looking forward to :/

Valve in a release delay shocker...

I just bought a new machine a the best monitor in the world for this game -- the NEC LCD3090WQXi. I've done so almost exclusively for L4D. I can stomach the two-week delay, but really I'm itching for it.