To pay or not to pay? Extra principal that is.

Here's the dilemna. I have a mortgage that month after month, I ask the question if I should be making additional principal payments toward it. Sure, it will be nice to get on the fast track of paying off the house. But that money could go to better use right, say.. investing it in a high return stock, but that's uncertain. Also if I do pay down the principal, my following regular payments would increase the principal portion that much more. That means my subsequent regular payment would have a lesser percentage riding on interest. This is good and bad.. Good, because I'm that much close to complete home ownership. Bad, there's less interest payment to write off on your taxes. There's differing opinions on the web, so I go schizo every month when staring at my mortgage bill..