Ok, Well I am going to compare the Desire as it will be with 2.2 to ensure this comparison is up to date:
positives
browser zooming auto refits text to view so no scrolling horizontally to read.
can download files from the browser.
can share files via blootooth
widgets
7 screens
customisable folders
customisable lockscreen
customisable app images
phone can be a portable hard drive.
not having to use iTunes for everything
larger screen
wifi tether
rooting is easier and safer than jailbreaking
installation on non market apps
removable battery (you'll agree when your battery dies)
google/facebook/picasa integration (teh sex)
FLASH
The fact that my phone can be completely different to yours (see post desktop thread)
cheaper
beta positives
- the link with desktop browsers, this is awesome
- the music streaming service
- faster web browsing
negatives
screen quality is slightly better on iphone 4
battery life may be better (not sure until used in practice)
better games right now on iphone
light on when video recording (although this will come soon, possibly only to rooted users tho)
Please feel free to question any of the above, and I will explain why i am right and you are wrong