IMO iLife should be part of OSX.
Why?
Because with Mac's things are supposed to "just work", you can make your home videos, create your own songs, build a website bla bla bla. The thing is, this is NOT a bundled feature of OSX, if you buy a used Mac and decide to get Leopard you have to 75$ on top of it just to create the kind of content that Apple makes sound so "native" and "out of the box".
I'm just saying this because, when I took the plunge and bought the 24" iMac, I only knew afterwards that iLife was bundled with every Mac purchased but not with OSX itself. I was reading a OSX Vs Windows comparasion chart and a lot of topics won or tied by the PC side were like "No native photo editing program", and I was like "what about iphoto?" oops, not bundled with OSX.. And more examples that prove OSX has much more value with iLife inside, check them out if you'd like:
www.xvsxp.com
From what I know about Apple I think it's not like them to divide products when there is no real need to do so.
My humble opinion. It should be: Leopard (with iLife included) - 200$.
*As for the release date.. I've been saying June ever since the WWDC 07 date was announced