OS+apps(including games) go on one partition. Some games install files into the \Windows folder and when you clean install the OS, games previously stored on other partition won't work until re-installed. I keep a 60GB partition for that purpose.
How you arrange other partitions is up to you.
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Reply to wuzy
I'm not sure that your going to notice a performance increase just by partitioning. I always make a Data partition and then a separate OS partitions, for the convenience of data sharing and reinstallation. To notice a performance increase your going to need to have two hard drives.