Well for me is sort of a sad day but not for what you imagine. I grew up with my grandparents since I was 3 years old so I always considered them like my parents. Well so happens that my grandmother died on Valentines day many years back but I that is what it reminds me of every year.
If you read this I am sorry to say that you just lost 5 seconds of your life that you wont be getting back.*
Socially engineered, and I'm split between socially efficient (allowing both partners, notably male, to be more lazy during the year and then make it up all at once = less energy spent) and socially inefficient (leading to an increase of lazy partners who celebrate it for external reasons = more failed relationships).
It's like any other holiday, it's what you make of it. If people get some legitimate joy out of it, then that's great. It doesn't make me lonely...frankly, I don't think too much about it.
The only thing that bothers me a little about it is that the expectations are rather narrow, and therefore require little effort to produce. It's sort of like how people call New Year's Eve "amateur night", except it's about paying attention to your SO instead of drinking.
Everybody have fun tonight. Everybody Wang Chung tonight.