The bitcoin exhange rate could change dramaticly. This could affect you.
We could see a fork, where part of the user support the new size and another group refuse to use the new block size. Then will we have a big problem. And the exhange rate could colapse because of uncertainty.
A funky thing about this scenario is that you will have double the bitcoin, the coins you own at the point of fork, will exist in both forks.
But half of those bitcoin will be worthless! It will surely only be a nightmare if some exchanges decide to back one fork, and others the other fork.
It would stupidity too though, so I doubt it will happen, someone might try to keep the dead fork going for something though.
Good to know that I don't need to do anything, if every end user had to do something, I think it would be a big negative for Bitcoin.