@De-Void
While I don't use copy and paste every day, I use it often enough that I would miss it were I not to have it.
Multi-tasking is probably less of a big deal. I gave Apple a lot of props for their push notification system when they came out with it because I'm quite convinced that this solves the biggest problem that multi-tasking has traditionally been used to solve. I believe WP7 has the same type of system so that's good. I can tell you, however, that a few of the non-multitasking enabled apps on the iPhone are very annoying to use. Epicurious, for example, forces you to sit through a 3+ second splash screen every time you start it up. Yes, that is most likely the app's fault but if the OS had multi-tasking, this wouldn't be an issue at all. I also wonder what the effects of not being able to maintain a wireless connection in some apps when they get "minimized". For example, I use a couple remote control apps on my iPhone and I can switch away and switch back and I'm still connected. Not sure if that is thanks to proper multi-tasking.
But, I could probably live without those on a day to day basis, maybe. Of course, I can also live without notifications on my home screen and lock screen too.

No, for me the bigger issue is the lack of certain APIs in general, and no VOIP apps specifically. I have a Skype phone collecting dust right now because my iPhone
is my Skype phone. Unless I'm mistaken, there is no Skype coming to WP7 until the networking API is improved. That is a showstopper for me personally.
So I would say those are my killer apps: remote control apps that I need to be able to switch to instantly and Skype. Without those, I can't personally consider buying WP7. I have faith they will be coming within the next year though, I'm not worried.