[itsid]

If there is no hidden content in any post of a specific page it won't add any query.
If there is hidden content that is thanked for before it wont need any additional query either to show it up (it uses a variable provided by the post_thank_you_hack)
Only if that fails (see first post, flw) it needs to be changed to make an own query for those cases.
There is one query to check if viewer has answered already (if that option is enabled) that is called if hidden content is still invisible (not thanked p.e.)
So best case : No hidden content or all hidden content is thanked for (original plugin) = NO additional query
Worst case : Hidden content, not thanked (changed plugin for errorcorrection), both options activated, [not] answered = Two Querys per post (only those that contain the hide-tag)
Normal behaviour = One query per post (containing hidden content only ama)

Yes, I was told it works smoothly with 367, not tested myself

You shouldn't encounter any speed-problems not even with ajax-ability enabled,
If you do, you can try to disable ajax-ability first.
Uninstalling the hack won't leave a trace, because it's fully pluginbased (images excluded)

'sid