I've had my Giro G9 (my first helmet) since 01/2008 (label indicates mfg 06/2007) and have used it on the slopes ever since. I have the medium size and the In Form system is great for fine-tuning/snugging the helmet to your head. I'm not a fan of the matte colors, so I wound up choosing the shiny grey/titanium color. The color and shape make it understated which I prefer.
I sometimes wear a balaclava with the G9. A regular knit hat would not really fit under it. I'm just throwing that out there because I recently overheard a girl ask a salesperson if the cute ski hat she was buying would fit under a helmet. So you can still get that cute knit hat, but just save it for apres-ski!
The G9 keeps the your head warm, especially when using the enclosed Weatherstrip vent plugs. The downside of the vent plugs is that if you want the vent open, you have to pull out the vent plugs and store it in a place where you hopefully won't lose it. This is a minor inconvenience if you like to open and close the vents. I typically leave all the vents plugged, so this hasn't been a problem for me. If this is a breaking point for you, then I would recommend to go check out a higher Giro model that has the Thermostat ventilation control (open/close vents with a button).
You can easily pick up a G9 on sale, but the bottom line is that this is a great helmet. It's definitely worth it.