I think the simplest way to get the post history stuff done well is to have a few very simple filtered displays of their post history, perhaps 4 different things if you want to allow sorting by section. For example:

1 - Created threads.
2 - All Off-Topic section(s) posts.
3 - All RP section posts.
4 - All RP section posts in IC tabs only. <-- This one is obviously the key to easily skimming a user's IC posts.

They could be tabs, or links you click that sends you to a "search results" page, whatever works. Maybe a straight "all posts" history could be thrown in as well, but with #2 and #3 in place that might be redundant and not very useful. If you want to allow people to skim a user's IC posts in the literal sense of actually having them all presented to skim, you could make the posts be displayed like posts in a thread with the full text of each post immediately visible (or the first X lines with some kind of "expand this post" button) upon clicking the link/tab for viewing IC-only posts. If that's a pain in the ass, it'd probably be just fine for v1.0 if they simply got a list of direct links to the user's posts to click on, just like we get now in a user's profile. Less quick and easy skimming that way, but all the relevant data is still readily available for anyone wanting to view your IC posts.

For general organization, I think tabs work well. One tab could be Post History or something, and then, if this is a feasible thing, there could be sub-tabs that show up and give the above listed post history filtering options (which then has either the list of links or the actually displayed posts right there in the profile page). This same sub-tab approach could be done with other things in the profile, like a Roleplaying tab that has a sub-tab to show a person's interests and such to act as their RP Card, a sub-tab that lists what games they're already active in and whether or not they're currently looking for more games to join (and what kind, probably), and a sub-tab for storing character sheets if desired. It could also probably be used for the personal information stuff of a profile, maybe the general profile junk in one sub-tab and off-site contact details in another. Oh, and the stalker wall could easily do with some tab filtering very similar to searching for another person's post history: a sub-tab for threads your friends have made, a sub-tab for their IC posts, etc. I don't know if the tabs within tabs thing is easy to do, but that would probably make for the simplest and most intuitive user experience in the end.