I know I'm going to sound like a contrarian, but I'm considering purchasing an SSD or two for backing up my DVD and photo collection. I'll stick the SSD in an external enclosure and minimise the number of times I write to it, ie it will essentially be readonly. I'll add some voltage protection devices inside the case, if it doesn't already have any.
Obviously this doesn't make sense from a cost standpoint, but I'm more concerned with reliability than cost per GB. External rotating storage devices are very prone to mechanical shocks and high case temperatures.
As for speed, imagine how long it would take for a full format, or a complete virus scan, or a total backup, or a defrag, at 60 MB/s as opposed to 200 MB/s.
http://www.google.com.au/search?q=3+terabytes+/+(60+megabytes+per+second)+in+hours
http://www.google.com.au/search?q=3+terabytes+/+(200+megabytes+per+second)+in+hours
The difference is actually about 4 hours versus 14 hours.
Still another consideration is booting from a hibernated state. This requires that system RAM be restored from an image file on the HDD. A 4GB RAM image would require about 20 seconds at 200 MB/s, or 67 secs at 60 MB/s. (These times would be halved if the image were compressed.)