Sure its a lot of space, but like I said before - if you have a display that will benefit from uncompressed full 1080p content, and can swing the storage, it's totally worth it. I currently have a 10Tb RAID5 storage array that cost me just under $2k to build (12 1-Tb drives on a 3ware 9500SX sata RAID card in a Norco 4020 rack mount chassis). It would probably cost closer to $1k to build that same setup today. I've filled nearly 8Tb of that space with ~ 700 movies and TV shows. I'd say I have probably 30% BD rips in MKV format, and the rest are DVD rips (also uncompressed) with a smattering of compressed BD / HD-DVD rips, also in MKV format. I have room to add a second 8 drive array, and am planning on building that out early this year with 8 1.5Tb drives in RAID5 (approx another 10Tb after the RAID is built) - I already have the drive bay space and the RAID card, just need the drives
My critical viewing display is a 92" 1080p front projector - a panasonic AE4000 - and I can easily distinguish a compressed 1080p source from a native BD rip. There is also a very distinct difference between a DVD version and a BD one - hands down the uncompressed BD wins every time. XBMC in linux using VDAPU handles these full 1080p BD rips without missing a beat on my ION based systems. Good stuff!