I know how web caching works... the point I was really getting at is that forums present a unique challenge when it comes to caching.
Pretty much every page is unique to every visitor at any particular point in time since their content will typically depend on a set of state data that is unique to that user at the time the page is served.
My new posts page is unique to me because the content depends entirely on what's been posted and what I've read. Other content is changing constantly as well, like post counts, on/off-line status, post ratings, trophy points etc.
So, I stand by my statement that the best way to handle the new posts page is to move the ignore processing into the database. It's then being handled by a piece of software designed for such purposes (i.e. the relational database management system). The scripts which generate pages are built in a general purpose computing environment which does lots of things well (compared to the RDBMS which does a few things incredibly well).
So using this (obviously this is meant as an example)...
SELECT * FROM POSTS WHERE (NOT (USERID IN (1,2,3,etc.)))
That is the bread and butter job of an RDBMS.
Doing that has the potential to remove (if there are 200 new posts in the new posts page) 200 conditional branches (each of which has to iterate fully over what could be a large list of user ID's to be ignored). It also solves the problem of lots of spammers being ignored = empty new posts page because ignored posts won't feature in the record limit of the query (which I believe is 200 records).
I've spent a great deal of time optimising complex systems in order to improve their performance. Making the best use of the tools at your disposal is the first step. Use specialist tools rather than general purpose compute as in the vast majority of cases you can achieve marked performance enhancements (and in this case solve a bug), and quite often with minimal work.
All I was trying to do was explain why the issues with ignoring lots of spammers results in an empty new posts page if the spammers have been busy and have filled it with their crud.
RE: the system you mentioned, thanks for the info. Always curious about things like that.