The mega pixel issue is only one of the ones you need to think about. If you want to get some additional input, go to the following link and read away.
http://www.steves-digicams.com/default.htm
Typically, the question warrants a question, i.e. how large a print do you want to make? We have used a variety of digitals and the mega pixels (several other factors being equally if not more important) primarily limits the quality when you get into printing larger formats.
Too many people forget that the photos should be taken and preserved in a high setting and put on media storage before doing anything else. The greater the quantity of file data, the more you can do with the photo later. You can't build from a shallow base but you can reduce what you have. It never seems to amaze me when I go into PhotoShop or even Picasa2 (free download) or IrfanView what types of enhancements can be made if the file format and size have been considered.
You indicated you have been using a decent camera . . . probably already aware of the above. Happy shooting.
Steve