I just got a message from "Greetings.com":

Hello friend ! You have just received a postcard Greeting from someone who cares about you...

Just click here to receive your Animated Greeting !

Thank you for using www.Greetings.com services !!!
Please take this opportunity to let your friends hear about us by sending them a postcard from our collection !

If you "click here" it takes you to an executable at some web site. I don't know what it does, and I'm not in a mood to experiment. When you get an email like this that's generic (that is, it wasn't specifically addressed to you by name, and it doesn't tell you who sent the greeting) it's a good bet that it's spam of some kind. If you wave the mouse over the link, and it's a different link than the one it purports to be (particularly if the end of the URL is "exe") stay far away from it.

[Update a few minutes later]

Jeez. Talk about people who shouldn't be allowed on the Internet:

To see how easy it was to lure in users via Google's AdWords, Stevens bought the drive-by-download.info domain and placed an AdWords ad reading:

Drive-By Download

Is your PC virus-free?

Get it infected here!

drive-by-download.info

Stevens has run the campaign for six months now, with 259,723 ad displays, and says he has had 409 clickthroughs.

The ad has cost him only 17 euros so far, which by Stevens' reckoning adds up to €0.04 per potentially compromised machine. Most of the systems visiting the site, 98 percent, ran Windows.

"I'm sure I could get much more traffic with a higher Google Adwords budget and a better-designed ad," Stevens said in a blog posting.

Four hundred clicks out of more than 200,000 displays, on an ad that reads like somebody's idea of a joke? I wonder how many of the click-throughs were from people who knew full well what they were doing, figured it was a gag, and wanted to see what was on the other end of that link.

I suspect that a good number of those clickthroughs were simply accidental, in addition to what wolfwalker said.