I have always* found the System i Information Center to be extremely helpful with information about the System i platform. In case you've missed it, there is now a Sametime 7.5.1 Information Center. It appears to be something that all Sametime admins can use for some great information.
* - OK, for those of you who used the i Info. Center before around V5R2, it was pretty bad. But after they got rid of the slow java menus and cleaned it up some more it is much better.