I own both the N900 and an iPod Touch, and I DO miss some things in the N900, although it has definitely become my main mobile device. I did research "quite" a lot about the N900 before buying one, so I knew what I was getting, and don't get me wrong, I _love_ it!
But the mailclient in iPhone OS (although still missing some handy options) easily beats the standard Maemo5 client (Modest), and the Safari browser is a lot easier to use then MicroB (although the N900's bigger screen >> the ipod/iphone screen ). And yes, I know, iPhone OS doesn't support flash, but to be honest, up until now I haven't had a wonderful flash experience on my N900 either (dedicated apps like zoutube excluded)...

So what I'd like for device is the N900's hardware keyboard, better camera, ... with the future iPhone's probably better specs. And in my perfect little dreamworld that device would be running an OS that sports the openness (high mod-ability!) and everything else linux from Maemo, together with some of the benefits of iPhone OS (like better email client and such).

Then of course, these are just my two cents

Edit: I almost forgot! I'd want the OS to have a community like the one behind Maemo, because everything that's missing is, in it's time, being added by some great minds here! Thank you to all developers compensating for the out-of-the-box "shortcomings" of our N900s!

Dries