I tried a EHD for a while, but since I scrap on a laptop and I like to sit on my couch, I gave up on that pretty quick!
My computer is only a little over a year old - so I still have space on my HD to have all of my "good" kits on my HD with no problem. But I did beg hubby to let me get a NAS (Network area storage) device. It is hooked up to our wireless network, so I can access all of the storage space wirelessly just like an EHD but I don't have to be plugged in. Also, it has built in mirroring capabilities - I bought a 1TB HD on sale at Amazon a few months ago to go with the one that came with the NAS...so now I have 1TB of mirrored (backed-up) storage!
For anyone interested - I have a Ready Nas Duo...it also has an FTP site, a web server (so you can host photos and web content), and a bunch of other stuff. I LOVE it!!