Similar Threads are generated upon creation of a new thread. They run one tough query when you create a thread, and store the results. Then it runs one VERY LIGHT query to display them to get the live reply counts. It won't bog down your server at all.
vB3 processes a lot more data (permissions, settings, cached data, etc.) than vB2, and does it much faster than vB2. That should tell you that it's a major speed and load improvement.
At first, hacking vB3 will give you headaches, because there's many more things to take into account now: phrases, different permissions, optimization, caches, and tons more functions to automate processes everywhere. However, hacking vB3 will teach you more efficient, advanced coding, and pretty soon you'll discover that vB3 has been created in such a way that Hacking it is a BLISS. a Gift from the heavens. Tons easier than vB2 once you get the hang of it.

And I can know, I've done some serious vB3-hacking already ^_^
Hacking vB3 is so nice that I have refused to do any vB2 hacking ever since I started hacking vB3.
The vB3 engine is about 4 times more easy to use and customize, and infinitely more flexible. Seriously.
