upgrading unstable -- 44 packages held back?

[Kurt Lieber <debian@kirpatrick.com>]

I'm running unstable and when I do an apt-get upgrade, it tells me it's 
holding back 44 packages. (a lot of which are related to kde, which I'm 
assuming is because I'm still running 2.2.1)

If I do dpkg --get-selections |grep hold, I see the only thing with a hold on 
it is my kernel-image.

So, I'm assuming this is expected behavior, but can anyone explain how the 
determination is made to hold back certain packages?  If it's not the hold 
flag, what else does it look for? 

Also, how do I upgrade those packages?

Thanks.