The big one is the search and that's the first query that you posted. By default we use MySQL's fulltext indexing and by looking at your query it looks like it's searching all of your posts (there is no date limiter in there). So it will search through all 1.25 million posts. That's definitely going to cause some pretty big slowdowns. I'd make sure there is a reasonable range on the time that users can search as normally it should just be searching through a portion instead of all of them.
The second query is just grabbing the 25 newest topics for a particular forum. That should normally be a pretty fast query. That might be slow if you have a forum with a very large number of posts and it's set to display all of them, since even with a limit clause MySQL still has to search through all of them to find the 25 newest. You can usually speed that up by changing the default to only show like the last 6 months or year by default.
