How To Manage a Collection of RAW Image Files, Cloud Backups?

I am a digital photographer and archivist.  At work, my digital photography
workflow is largely dictated by a multi-user networked environment. In
addition to myself, I have at least one (sometimes as many as three)
people adding and editing metadata on a collection of over 45,000
images, growing at a rate of 1,000 images weekly.

Adobe Lightroom won't work because it cannot handle more than one
person editing photos and metadata at a time.  Lightroom also doesn't
particularly play nice with networked volumes, either.  Our tool of
choice was iView Media Pro (IVMP), but that puked once our collection
reached around 30,000 images (it cannot handle a database larger than
2GB, including thumbnails).  IVMP also isn't really a multiuser editor,
we used it via Remote Desktop (RDP) on the server, allowing one person
at a time to do work.  It was really kludgy and I was rather happy when
it broke.

Now, we are using IDImager, a
very reasonably-priced photo metadata editing and import/export package
that is truely multi-user, via a database backend.  It feels slightly
laggy at times, but it is fantastically aware of external metadata
changes (made via Bridge, for example).
 
Anyway, back to my personal digital photography workflow, which I
have largely ignored over the past year as we refine things at work. It
should be much easier to deal with, at least in theory.  With my recent purchase of a MacBook, I am taking a fresh look at my own personal work habits.

Goals:

• Leverage the power of Adobe Lightroom as the
  cornerstone for my operation, including acquiring/ingesting, tagging,
  adjusting and finding images
• Avoid the $700 purchase of Photoshop... or at least postpone it until absolutely necessary
• Maintain a safe, yet sane backup scheme involving at least two,
  ideally three, physically and geographically redundant copies of all
  RAW images

Here's what I have in mind for my image archive: 
Maintain a master set of RAW (DNG/JPG) images on my always-on Vista
Media Center PC. This master set will be updated via rsync/ssh from my
MacBook which is connected to an external hard disk(s).  This seems to
be the best hybrid approach to having physical access to my RAW
archive, without the danger of physical damage or loss, as files are
automagically backed up to a hard disk in my living room.

As added insurance against the worst case scenario (fire taking out
both my Media Center PC and external hard disk(s)), the Media Center PC
will push my RAW archive to Mozy.com,
creating an offsite backup in "the cloud."   Mozy offers $6/month for
"unlimited" backup space; It is cheap insurance against the unthinkable.

After one week of continuous backup, I have about 15GB (5%) of my
RAW archive in Mozy's cloud.  I also plan on backing up my documents in
a similar manner, but leveraging OS X's Time Machine backup to external
Harddisk.