I have an 06 GS. I got it in October. I use it as a daily driver, but my office is close to the house, so I have only put on about 3,600 miles. There is no difference between the '05 and '06. I only got the '06 becuase I had time to custom order it last summer. I did not have an extra spot in the garage so I waited. The dealer would have discounted an '05 at the time.
There is no better daily driver on the road. period. end of story. You can not drive a ferrari as a daily driver. You drive it to drive it, not to go somewhere. The GS is as reliable as any porsche, M-BMW, or AMG MB I have owned. I have not had the GS in the shop once. It runs great, sounds great, and even in Los Angeles, I have only seen 2 on the road in the last 12 months.
I will be as excited to make my 6 mile drive to work tomorrow as the 1st day I got it!
good luck.