I've never really run any of these solutions at home myself. The WD is just something I've kept my eye on if I was thinking of going that way. Currently I have a Tivo HD which I can "push" video files to if I want to view them, although I take care of most of my viewing needs via the tivo, fios, and netflix.
Are you backing up DVDs to VOB files and want to watch them? If you don't mind going file by file I think you can just use a usb flash drive to bring things over to the WD as you want to watch them.
The nice thing about the LaCie is that it has a built-in hard drive so you could hook it up to the mac and copy everything to it and conceivably it should work without any meddling from there. For $100 more, maybe that would be easier.
Both are networkable, which means either getting a powerline ethernet device or USB wifi solution. I use a powerline ethernet hookup with my tivo which works pretty well. But this adds more $$ to the cost.
Maybe poke around here:
http://www.avsforum.com/avs-vb/forumdisplay.php?f=39