To make a quick mention of a repeating point in this thread... the reason no one is talking about Drift Mode in GT4 is that we simply don't know anything about it. All we know is that it's there... that's it. Doesn't really give folks a lot to talk about.
Me, I can't drift to save my life, I've tried.. hehe. At least as far as exhibition drifting goes, where (as mentioned above), the car's never pointing straight. I will, on occasion, hit a corner a little too fast and a little too sharp, in order to break the rear free and slide around it. Which I suppose is technically "drifting", but it's not exhibition drifting. But it's the type that I prefer.. high-speed, having a grand ol' time slinging the car around corners. Not necessarily going for length or high angle. And I only do it in Free Runs, never in a race, unless I accidentally come into a corner too hot (and, as mentioned above, I'm able to save it when the car starts to slide).
A good example of what I typically do is what Stefan Rosier does in the "Faszination" video, zipping the Ruf Yellowbird around the 'Ring. If you watch it, he's not doing exhibition-style drifting, he's just slinging the car around the corners. And yes, I plan to get a Yellowbird in GT4 and try to do what he did.. hehe.
In regards to the pluses and minuses of drifting, it really depends on what you're after. If you're trying to win a race, it's probably best to hold the racing line, grip-style. You'll get faster times and less tire wear. If you're just out on a Free Run to have a grand ol' time zipping around the track, then have at it, do what you will.
I think it was best summed up by Stefan Rosier himself, in an interview.. I found this quote a couple days ago. One of the interviewers asked him (paraphrased) "Why do you drive the way you do? Isn't it faster to drive normally?" To which Stefan replied:
"Well, when you make love, you're not always trying to make a baby..."
Not only is the comment funny, but it's also very true. There's more to driving than just getting the fastest times, just as there's more to lovemaking than having babies. To the folks that argue that drifting is slower: You're right, but I'm pretty sure you're preaching to the choir... the drifters among us know that drifting is slower, especially exhibition drifting. And in a race, I highly doubt that they use it. In fact, were GT4 online, you'd probably never see them doing any fancy drifting, unless the race was decided ahead of time as a drifting competition. Racing and drifting don't go together, and I think everyone here already knows it. But driving and drifting is another story. It's all about going out on the track and having fun, not necessarily about getting the best lap time.