The blog post is long, but very good. Definitely answers all your questions, and the ones you'll ask afterwards.
WRT CUPS and networks, look at the posted messages after the blogpost itself, there are some interesting notes there about it.
The proof is -- as usual -- in the pudding, but the design of systemd seems good, and simplifies things a lot. If it is available for F14, I'll switch to it.
My only worry is the idea of "writing init scripts in C" -- I think it's hyperbole to indicate that you just write a config file, and a C program (systemd) does the right thing. That misses the overrides you can apply trivially in most linuxen by creating /etc/sysconf/$servicename or just hacking the damn initscript.
AIUI, you can just point systemd to an oldstyle script anyway -- that loses the parallelisation and fast-boot properties.
Maybe systemd can provide a low-overhead init script interpreter? Python? Lua? How to do it would be a challenge -- you don't want an embedded interpreter in systemd, but you don't want the startup overhead either.