How come certain websites are loading slowly?

[b]

I asked a similar question earlier today, but I have more info now:

For the past few days certain websites like Yahoo, Google, and YouTube were loading really slowly but other sites like MSN, Facebook, and Amazon were not. When YouTube finally loads all the videos are blurry. I reset my modem and router and everything worked again for about 5 minutes before it started slowing down again. Before I reset them, the longer I was online the faster things got (but it took a while) but now the longer I am online the slower it gets.

I'm starting to think my internet provider is having issues right now instead of my computer. I ran virus scans and that came up clean too.

I'm hesitant to include this, but someone mentioned that maybe the reason why certain sites are slow is because they have an increased amount of traffic because of the Olympics (I did notice that all the sites I'm having issues with have some sort of coverage or additional attention to the games).