Well, in my office we only have one guy, and there's no way on God's green earth he will ever have a child. If I was ever in a situation where we did have a guy, I would definitely have a shower, but I would make it "manly". Have food like wings, nachos, etc, not little sandwiches and such. No fruity punch, although what is a "manly" drink other than root beer? I would suggest that we do gifts other than cute clothes (although certainly people can buy whatever the heck they want!); the diaper shower idea is good. And I would definitely invite the mom-to be.
While we had a baby shower for my sister, my brother in law's friend had a "shave" for him! They took him out for lunch, had some guy time and presents. He really enjoyed it!