People often ask "What has Obama done". That is actually a pretty simple question to answer, and for a lot of people that answer is enough.
Here it is, with a comparison to one or the other of his competitors:
Obama has kept the same principles regarding on abortion; in '99 McCain was against overturning Roe v. Wade - in 2006 he favoured overturning Roe v. Wade and returning control to the individual states.
Obama has maintained that invading Iraq was a mistake; Clinton originally voted for it, and has had to modify her stance a number of times.
Obama has maintained a squeaky clean record since he started serving as a Senator; McCain was investigated as one of the Keating 5...and don't get me going on Clinton.
The long and the short of it is that people like Obama because he has not show the same level of corruption, flip-flopping, and dishonesty that his competitors have shown. He has had a pretty consistent and squeaky clean image on the national level. He gives them hope that there might actually be a politician who wants to uphold American values. His competition cannot offer that, and that is the 'change' the people want.
Most people don't examine issues - they would rather vote for the person they 'like'. Most people can't explain why they 'like' them though. Based on that observation I had Obama picked as the Dem candidate a couple of years ago. I'm still sticking by that prediction.
Personally, as I don't trust any politicians, I think it is only a matter of time before people start finding/examining (it has already started) the skeletons in his closet. Combine that with the level of power he would have and he would end up just as corrupt as any other Washington weenie.
Edit: Oh - I'm still voting for Ron Paul!
Steve