My home network/storage needs are changing and I am searching for some opinions and starting points on what a good network/storage layout would be that can serve my needs for a few years into the future. I think I have a decent starting point for equipment, but I am also willing to invest fairly heavily in a solution that can last me for a while. I am a bit of a tech nerd and I have a moderate tolerance for setup of the solution. I would prefer if maintenance of the system is somewhat low once it is setup, but I am willing to accept some tradeoffs.

Existing equipment:
Router - Netgear WNDR3700 (gigabit)
Router - DLink Gamerlounge DGL-4300 (gigabit)
Switch - 16 port Trendnet green switch (gigabit)
Switch - 5 port Trendnet green (gigabit)
Computer - i7-950 office computer (gigabit ethernet)
Computer - Q6600 quad core media center, hooked up to TV, records shows (gigabit ethernet)
Computer - Acer 1810T ultraportable laptop (gigabit and N ethernet)
NAS - Intel SS4200-E (gigabit) External hard drive - 2TB WD Green drive (esata)
All kinds of miscellaneous network connected TV, Bluray, Verizon network extender, HDhomerun TV tuners, etc.

Requirements:
-Robust backup solution for a growing collection of huge family picture files and personal files, around 1.5TB. (Including offsite backup)
-Central location for all user's files, while also keeping them secure from each other.
-Storage for terabytes of movie backups and recorded TV, and access to them from all computers (maybe around 4TB eventually)
-Possibility to host files to friends and family easily

Nice to have:
-Backup of terabytes of movie backups

Intriguing possibilities:
-Capability to have users' Windows desktops and files look the same from all network computers

I am not sure if the new Windows Home Server 2011 would fit into this well, if I need a domain server, how best to organize my backups, or how to most effectively use RAID. Currently I am simply backing up all computers to a RAID 1 on the NAS box, which I was thinking could prevent a situation where I reach for a backup and find that the disk is corrupt.

One possibility that I am thinking about now is simply using my media center PC with a huge RAID of hard drives on which all files are stored. Pseudo-backup of all files would be present because of the RAID, but important files would also be backed up off site via carrying hard drives to work. But what if corruption seeps into the files and the corrupted data is then backed up? Does RAID protect against this? I really want to take next to zero risks with the irreplaceable files. I can handle some degree of risk with the movies and other files.

I'm looking for critiques on this idea as well as other possibilities. To summarize, my goal is high functionality, media capable, and robust backup of irreplaceable files.