LJ has these instructions posted in their Troubleshooting section ... personally I habitually clear the cache on my computer weekly, plus I have the settings adjusted to look for a new version of every webpage and not to use the cache, but ya gotta be able to tell 'em you did this before contacting support. I'll also be checking all my buddies' LJs direct over the next couple of days to see if there's anybody else whose posts I've not been seeing, just in case this is a wider spread problem ... I'll let you know if you, too, are part of the lovely online weirdnessnessnessness.
EDITED TO ADD: Okay, as catdesk, I've reported libwitch's inability to see my new posts on her friends page to LJ Support. I've also asked them to let me know if they'd prefer the nonviewable reports to come from those who can't view ... I'll post it here in my LJ if it turns out that's what they'd prefer.