Technically, multitasking works fine, but there is no easy way to switch between tasks. I wasn't referring to the capability, but the user interface implementation.
Really, 75% of the problem is the lack of tabbed browsing(midori doesn't count).
With the Pre you can just do a gesture to move between cards, side to side, or gesture up to zoom out and see a bunch of cards next to each other and tap one to maximize it. It is just so much more intuitive and it just sort of flows. With the n800 I always get the feeling that the OS is getting in my way.
BTW, I took side by side pictures of my n800 display compared to a simulated iphone display on my desktop LCD to see the difference in resolution. Obviously it isn't apples to apples, and the technique isn't perfect, but I think the difference is big enough that it is still a useful comparison