Well here are my impressions on the Nexus One after I switched from the iPhone 3GS (Jailbroken):
Pros
-Screen is absolutely amazing. It looks so much better then the iPhones screen, this is no contest. Colors are vibrant and text is extremely easy to read.
-Hardware wise it is no contest in comparison to my 3GS. 3.7" AMOLED, 1GHZ Snapdragon processor, 512MB Ram, 5 Megapixel camera with LED Flash, Trackball (lights up colors for notifications). The overall feel of the phone is excellent and feels like you do have a expensive device in your hands (really nice quality).
-Customization is absouletely mind blowing. I have widgets on every screen, pictures of my loved ones, shortcuts,folders,directions and so many more that each screen looks different and very informative too (RSS Apps,Facebook Widget,FML Widget

,etc)
-The notification system is darn right awesome!. I am literally in love with how it works and how fluid it all is. I can see so all my notifications from literally any app and best of all it doesn't interrupt you or is annoying (contrary to Push Notifications). The live wallpapers make the phone that much more beautiful and the hundreds of ones available to download make me even more happier.
-Multitasking is very efficient because the Android OS handles the backgrounded apps very nicely and don't see a impact on my battery life.
-The camera and LED flash are very good. Awesome how you can share your pictures to other services (Facebook,twitter,etc) straight from the gallery (pictures app) and all the options you have before taking the picture (negative,black and white,etc).
-The trackball is very useful for notifying you at a glance that you have something pending (missed call,new email/sms,etc) and its nice to navigate with at times (a break from swiping so much).
-Apps are able to use any part of the OS and hardware making them that much more better!.
Cons
-Touchscreen not as responsive as the 3GS but it is not bad at all.
-No dedicated camera button
-The bottom 4 capacitive buttons are not 100% accurate. This is solved by tapping a little above them and they work every time like that.Hopefully they can solve this in a software update,if not whatever.
-While the music player gets the job done, it doesn't look as nice as the iPod found in the iPhone
-The quality of the apps (mostly games) are not as good as the iPhone's.
All in all I am extremely happy with my Nexus One. It truly is a huge step ahead of the iPhone 3GS and if any of you are scared of switching don't be. This is a amazing device and is well worth the money.