When my sister first told me, I had to immediately thank her since I know already what I'm going to do for her Christmas present (obviously, baby stuff - possibly even spring for a crib or stroller). As an added bonus, though, this past weekend my sister also showed us all her first round of sonogram pictures. I got to see the first images of my future niece or nephew....which all looked like a bunch of shadows and blobs (I swear, I never have the slightest idea of what I'm looking at in these things).
I've already decided on being that type of uncle who will take his niece or nephew to a baseball game when the kid is old enough, and promptly feed the kid a healthy dose of cotton candy, hot dogs, and soda. Then just as all that sugar kicks in after a couple hours, I hand the kid back to my sister, and a sugar-induced frenzy ensues. I also plan on buying the loudest, most obnoxious presents for birthdays and Christmas, such as Rock Band. Oh yes, I will relish this.
I suppose karma could come back to bite me in a few years when I have kids of my own, but that's something I'll deal with when the time comes along. Right now, I'm very excited for my sister, and even though a baby wasn't something she had been planning on for a while, I think she's warming up to the idea. My parents are absolutely giddy over the idea of becoming grandparents too, so I'm sure they'll give any support they possibly can. That has to be comforting for my sister, especially in the long run.