Is it really this easy?
 

I found this on you tube. I never did a water pump and would like to know how, but this piece just makes it look too easy................

http://www.youtube.com/watch?v=E-uzQi7IgwU

They dont show the guy struggling with the one bolt that is always stuck and rounded off that takes 3 hours to get out, but yeah, its that easy.

that was great. Just don't put the gaskets on wrong like he did. The merc water pump kits come with a lot of different gaskets because that style pump also fits the sterndrive as well. So pay attention to which ones you need. And make sure you always rotate the shaft clockwise or the impeller might become inverted. You also need to scrape the silicone off behind the water pump. Just before you reinstall the lower unit apply a new bead of silicone. This helps keep the water pump under water so it is less likely to lose prime. If you are in doubt I suggest that you get a good service manual. Just don't rely on some random guy on youtube.

While I had mine apart I replaced both seals under the pump. They were worn out and was leaking water into the gear case. Putting the cover back on the impeller is a little difficult. If you noticed there was a cut in the video while he was doing that part. There are torque specs for the water pump housing nuts also. It's not as hard as some people think it is.