The NYT published this article about megapixels back in 2006, but it still applies today.
How many Megapixes is enough? Well... not as many as you think.
For years, I've been saying that 4 Megapixels is enough for nearly anything that regular consumers would need to shoot and print. I still say that. People think I'm crazy, especially when they look at my camera. First question I get is... " That looks like a nice camera. How many megapixels is it?" My reply is always: "I don't know. I don't care how many megapixels it is. What's more important is the quality of the lens and the knowledge of how to use the camera appropriately. " I usually lose them after that. By the way, I still don't know the MP rating of my camera, it's a Canon 40D. 10MP?? 12MP?? I don't know and I don't care because it doesn't matter.I have more money spent on lenses than I do on the camera itself. When I'm shooting real estate in my home town of Minneapolis, I use the Canon 10-22mm lens. This lens costs about $700. That's more than I spent on the camera body.
So everyone wants to know the answer to the question: How many megapixes is enough? My answer today? 4 Megapixels is enough if you plan on printing up to 8x10 photos, or 11x14 photos. If you plan on printing higher than that, you may want to get 8 Megapixels.
The next qustion is usually something like.. "Well what about 15 Megapixels?" My reply? "You don't need it." "But, everyone else has it, and one of my friends just got 18MP," they say My reply? "You don't need it. Unless you are doing wall size prints. Besides, it will take up more space on your hard drive to store larger photos." Then they run out to the local big box store and purchase a 15MP camera anyway. Go Figure...