If you're planning on working with adsense, I've heard that one needs to be running 50 good content sites to make a good profit. That's not 50 pages is it? You mean 50 sites?! Good gravy that would take forever!
No, that is not true. I'm not sure who told you that, but they're an idiot. The owner of DP makes over $10,000 a month. The owner of Plentyoffish.com (who runs the site from his apartment) makes about $300,000 a month. One site, that's it.
if you have 50 avg sites that get a few clicks a day and make a few bucks you will need 50 sites to make decent money or if you have 1 or 2 really solid sites with great traffic you can clean up on that....it's all about the type of site, the quality, the traffic that determines how much you can make