I bought the 500GB version of this from Amazon in August 2007 for about £140. The "One Touch" aspect never worked properly but I have Syncback software which I use to automatically back up my files. (I backup all changes every evening and a full backup once a week as I use my pc for business).
This setup has worked fine for just over 4 years but now the drive is playing up. It is starting to drop files e.g. a folder containing 16GB will be shown in Explorer as empty. If I power the drive off and on it comes back. I think this is probably the beginning of the end and I expect a catastrophic failure at some point. Certainly I can no longer rely on it for backups. I have used it to retrieve the odd accidentally deleted file but never to recover an entire disk after a major crash for example. Sods law says my main disk will crash and I won't have a backup unless I get another unit. The norm now seems to be 1TB but I think I will get 2 x 500GB and swap backups between them for additional security.
I am disappointed it is giving up now after only 4 years in service - I think it should last longer and also the One Touch failed very early on so I give it three stars only.