I've had mine for 2 and a half years and I've had no problems with it, until recently. The shifter sometimes starts to act up, both in sequential mode and H-gate mode.
In sequential mode it will sometimes shift on even the slightest touch of my hand - and I really mean a slight touch - sometimes several gears at once, very rapidly. This is obviously very annoying if you're in a close race. Only happens on upshifts.
In H-gate mode sometimes it just "jumps" out of gear, mostly when I'm in second gear. For example when I'm taking a corner in second gear, it will suddenly just jump to neutral in the game, although the stick will still appear to be in second. I then have to give it a little pull and it'll shift back to 2nd in the game, so I'm guessing it's a faulty contact wire or something.
These problems come and go, though. However, it is no secret that the shifter on the G25 is by far its weakest point. I'll buy a better seperate shifter when I've got some spare cash and more time to spend racing.
All in all, though, I'd say the G25 really is great value for money. Keep in mind that I've used it frequently for 2 years with no problems whatsoever.