Staying longer than allowed- the conseqeuences

Just curious, not just for the UK but for anywhere, what are the consequences if you stay longer than you're allowed? I don't plan on it or anything, I'd never ever wnat to risk screwing up my passport- it was just a question that came into my head and nobody seems to know. The best friends and I can figure is you get banned from a country. Anyone know for sure?

Oh, and nice to meet you all 

My husband overstayed his visa in India in 2004.  He had applied for an extension but it was not completed (even though we were led to believe it was) and thus when we were at the airport ready to leave, they refused us exit permission.  He had to go to the commissioner where we were living and get explicit exit permission.

He didn't get banned from the country or anything. 

The consequences will vary alot, depending on the individual nation.  In some countries, you run the risk of not being approved for a visa in the future and possibly being denied entrance in the future, as well (if they catch on).