I bought a DFGT in late December last year, and used it for 6 months before I bought a G27. A DFGT is a great way to go for your first wheel. It is relatively durable, considering it feels the same way it does when I bought it, after using it at FF level 10 the entire time. The transition can be a bit tough though. I went from playing Forza 3 on a controller to GT5

on a wheel, so it may not have been as bad because I was learning to use the wheel at the same time as I was learning the physics GT5

(and around the same time, the GT Academy time trial). But, once you get the hang of it, the immersion is incredible and in my opinion much more fun. There is no way a controller can compare to a wheel when it comes to having fun in a racing game. Let me just say this: Forza 3 has not been played since the day the DFGT's USB cable was first plugged into my PS3, and I had immense amounts of fun with the Forza series, having played all 3 games. 3 great games, and they still can't keep me away from the awesomeness that is the Gran Turismo series.
However, it got to a point that I wanted even more control, more immersion, and I wanted to do it at a higher skill level. Not only that, I was starting to get annoyed with the DFGT's little downfalls I was annoyed with the DFGT shifting "paddles," which are just little buttons on the reverse of the relatively small diameter wheel wheel. I also got annoyed with the whining noise that the gears make (this used to drive my girlfriend crazy) as it can drown out the sound of the game when you need to keep it at a respectable volume. I was particularly unhappy with the pedals, as they were very cheap feeling, and lack any kind of weight or feedback. I saw the G27 for a decent price on Amazon, and went for it.
The G27 is all the things it sets out to be. The wheel feels great in your hands, the brake pedal actually has some weight, so you can rest your foot on it for left-foot braking. The gear noise is reduced
considerably and the wheel turns more smoothly. The first thing my girlfriend said when she saw me using it was "It's QUIET!" The wheel is slightly larger in diameter, but it is a welcome change. While the Force Feedback on the DFGT was never really an issue (I was actually pretty surprised at how strong it was the first time I used it), the FF on the G27 feels even better. In my opinion, this is due both to the smoothness of the gears and having 2 motors as opposed to one. However, neither wheel is too strong, as I've had FF set to 10 for both wheels from the start. The gear shifter adds the level of immersion I was looking for, and I've been trying to learn heel-and-toe braking. I never used the sequential shifter on the DFGT as I felt it was too close to the wheel and I didn't enjoy the feel of it, so I can't comment on the lack of one. I just use the paddles for all cars that are semi-auto/sequential IRL and clutch and H-shifter for all that come manual IRL.
However, having now used it for around 6 months, I am finding faults with it as well. Of course, it is not fully compatible with GT5, and I was fully aware and prepared for that. I knew that it worked with Prologue and the GTAcademy demo, so I had reason to believe that it would at least work with GT5. However, being unable to change button layout is annoying. Using a cars horn is just completely unavailable to me, so I'm missing that part of the game which isn't a big deal in A-spec, but I think would be nice to have online for notifying people of a pass, etc. I do miss that ALL of the buttons of the DFGT were on the face of the wheel, giving it a slightly F1 look. It could also be laid out as you wanted, and had a horn button with a glowing GT5 symbol which I liked more than the Logitech logo. I didn't think I'd miss the RM dial (the red dial, not sure if that's the right name) until it was gone, as the TCS and ASM setting in GT5 are saved either by car or by event, I'm not sure.That means if I forget to turn off TCS and ASM before I start the race, I have to quit the race and completely reload it again before I can change them and race. I've wasted a lot time because I hate driving with them on. I learned from the start with a wheel on Simulation setting, TCS and ASM at 0 and ABS at 1, professional physics, and manual transmission, so there wouldn't be a learning curve later when I wanted to learn to drive with them off.
There are pros and cons to both wheels. I enjoyed both, but the G27 is now my main wheel. I've been trying to sell the DFGT, but the price has been going down here and I wouldn't make all that much. Gonna try to sell it to this guy in Australia from GTP, because even with the added shipping, it will be much cheaper than a new one there and I'd like to provide another avid GT fan the opportunity to learn a wheel. If you have the money, I'd go for the G27 or I'd wait until full details about the Thrustmaster came out (the $500 dollar price point Kaz gave could be the Japanese price, as has been speculated. A G27 is 68,880 yen on Amazon.co.jp, which is over 800 USD, so take that into consideration). If you absolutely can't wait, the G27 and DFGT are both great wheels for the money, and it all comes down to price point and brand reputation. I chose Logitech over Fanatec in the end because Logitech is a bigger company and therefore has better customer support. I've heard some unfortunate things about Fanatec support, and if I ever needed to get it fixed I'd have to ship it to Europe.
I hope this helped, and didn't just end up being a long winded rant.