I don't like it.
Taking advantage of people's good-intentions and kindheartedness as a marketing scheme is going too far. If Western Digital really cared, they would just donate the money themselves or give a portion of EVERY purchase to a breast cancer charity.
If consumers care, as indeed they should, they ought to donate money themselves. I didn't feel so strongly about this until I met a group of breast-cancer survivors (just a couple of weeks ago) who are outraged and disgusted by this sort of practice- enough to organize against it. They feel as though these corporations are capitalizing on their suffering simply as a way to advertise and sell more products.
They aren't opposed to it in theory, because any donation helps, but the way in which it is presented. It more or less comes down to a "buy this car or we'll club a baby seal" mentality. If it were simply a normal part of their advertising campaign stating a portion of every sale goes to a charity, that would be okay. However, having a separate, temporary 'pink' line of products is insulting. It implies consumers ought to buy EXTRA stuff they might not otherwise to support breast cancer charities.
Rather than buying your girlfriend a pink hard-drive, why don't you donate $100 in her name to a breast cancer charity and buy her a normal hard-drive. Or, better yet, something she actually wants.