What can I say, car threads attract me
I'm going to have to side with Brandon here (Sorry Viper

...), the 550 just doesn't do anything for me. And I'm so glad BMW killed the 850, it was an overweight, underperforming expensive POS.
The 355 was an extremely beautiful car, however it can be outperformed by a stock 996 in many situations. From those that have owned it however, the F355 is generally considered to be more fun to drive than any Porsche.
Now the 550 is a more powerful car than the 355, but the thing is just too bulky and the looks, again, just don't do it for me.
Once you factor in the 360, the most beautiful car ever made, the 550 begins to look more and more like an ugly duckling. The only good thing about the 550 is its interior build quality, which dwarfed the 355, but luckily the 360 helped to bridge that gap as well as the performance gap.
Just my $0.02, oh and btw, F360 Spyder = mmmmm....
Take care,
Anand