just look at Google - it searches TWENTY MILLION pages in half a second
Sounds funny, because: a) Google is not using mySQL of course (and NOT ANY DATABASE at all, they are using their own data structure saved in a single files) b) Google have many hundreds, if not thousands, servers worldwide.
We for sure are interested in optimization, but as I said in very beginning - our forums is FOR SMALL AND MEDIUM sites, and it is exactly because of these reasons of optimization.
As about indexes and fulltext too - mySQL is not very optimized to work with them. I had, for example, one tourism database with just about 100,000 records - it was very well-structured and indexed, but these guys came to me and asked: what we did wrong? One simple select request costs us 22 seconds! The reason is if you combine statements like GROUP, ORDER, LIMIT or use altering tables like where Tb1.field1=Tb2.field2, mySQL will not as fine as it would be.
As I already said too - FULLTEXT might be a good idea, if it would be fully supported in mySQL. For now, it is only experimental stuff, and we have no idea what happens further. Developing a free program, we would not to make pain ourselves rewriting the script each time when database version changes (as it happens with PostgreSQL - fcuk, these guys are crazy, each new version has another SQL syntax).
You can try of course to optimize something with indexes in mySQL, and we would happy to know if it will help you (so we can use your excellent advices). But as I might expect, the solution is not to optimize mySQL. Solution is somewhere else.