[kh99]

Well, the forum cache uses the datastore. You can use it by calling function build_datastore() like:

$mydata = array("some data", "more data");
build_datastore('mydata', serialize($mydata), 1); // '1' means automatically unserialize when reading

Then to load it, create a plugin using hook init_startup and code like:

if (THIS_SCRIPT = 'somepage')
{
   $new_datastore_fetch[] = 'mydata';
}

and your data will be in $vbulletin->mydata. Of course you can use more script names in the if, or leave it out completely, depending on what pages use your data.

Using the datastore that way will actually add one query to each page if no other products are using it on the same page. Also, obviously you can't do a query on the data. If you really have something you want to store that could be different for each user, then you probably don't want to use the datastore (unless you don't have many uses and aren't worried about it scaling).

There's another cache system used by the CMS, but I don't know the details of how you could use it. And I don't think it would eliminate extra queries either (well, at least it will require one to use it).

If your only goal is to eliminate any extra queries, you might be able to add your data to an exitsing table, or create a new table, then add it on to an existing query, depending on exactly what you're doing.