1. InTrade is the same service as Tradesports. They both go back to the same help telephone numbers.
2. InTrade/Tradesports is run out of Ireland. I don't know if this implies a European bias in usage.
3. To the extent that InTrade is self-selecting like on-line polls, rather than random-selected like polling firms, you can assume that InTrade is biased towards the preferences of people who choose to use the service. Are on-line gamblers risk-takers or are they more risk-averse? Is risk-taking / risk-aversion a liberal/conservative trait? Does betting on sports and elections bring out a different kind of risk profile in people than betting on stocks (on-line investment portfolio software)?
4. Someone once suggested that a person like George Soros could throw some money at InTrade bets just to make it look like InTrade traders favor one outcome over another (since the potential loss of funds would mean nothing to a person like Soros). Since pollsters like Rasmussen use InTrade as a source (among others) when predicting which way a state will go in the Electoral College, once can presume that a wealthy person with money to burn would see this as a cheap way to influence public perception.
Hope this helps.
-PJ
The more someone like Soros tries to game the system contrary to actual results, the more people are going to jump into the market to profit by his efforts.