Downs: No c&p, no third party multitasking, no flash, somewhat buggy (marketplace crashes for me sometimes, heard issues about the alarm clock but haven't experienced anything regarding that), camera doesn't save settings
Ups: Marketplace is growing fast as hell, slick and fast as hell, pretty customizable, xbox live integrated, good looking games, live tiles are awesome, zune pass is fantastic, facebook is hella integrated if you're into it and copy and paste, third party multitasking and flash are supposed to be in this year.
It's a nice middleground between iphone and android. I have the htc hd7 and it's the best phone I've ever had. It's a really polished, yet pretty customizable os. browsing on it is also so fucking comfortable. webpages render correctly and it's smooth to zoom in and out. also, the touch keyboard is so fucking good and precise.