Why the people will use PunBB?

Heh, touche.

It's not a matter of PunBB being superior to all other forum software - because it isn't. It all depends on what you want from your forum, and the preferences of you and your users. Check out PunBB's about page. If you like what you hear, then yes, PunBB is probably the best choice for you. It all depends on what you want to do. For most sites that want a fast, easily used forum, PunBB is great. However, if you want a forum software including "everything but the kitchen sink" PunBB might not be the best choice. If you're looking to create a large site based solely around the forum and want a ton of features, a great, fully featured board you might look at is vBulletin (just be warned, it will take up a lot more resources than PunBB, and is not free). And if you want to get hacked, phpBB might be just the software for you.

These couple sentences from the about page pretty much sum things up.

... PunBB is one of those alternatives.

And like af3 said, you have to see it for yourself. You're using a PunBB forum right now. If you like it as a user, then most likely you'll like it as an admin.

I suggest you look into these classes.

To reiterate what others have already said, PunBB is a forum. People think of Internet forums, and they think of private messages and calendars. When I think of a forum, I think of it as it's definition: "A public meeting place for open discussion."

If you want a forum, PunBB is for you. If you want other stuff, go with something else.

Please, let's be civilized, no need to piledrive each other

I chose it because phpBB was pissing me off with crashes and just mainly sucked. And because Smartys poked me alot to use it back then.

Thats not true, you just have to mod PunBB up a little until you get a decent site, for example, My Friend  Reines and I run a small community here http://www.syi.cc, at the time of me writing this, the forum stats are as follows:

SYI age: 57 days

Forum stats
Members: 1,831
Total topics: 5,335
Total posts: 78,227

Members online: 7
Online today: 538
Guests online: 1

WhatPulse stats
Rank: 110
Members: 92
Keys: 153,842,006
Clicks: 71,737,402

There arnt very many people online as its 3 am atm

...but not everyone is willing to spend the time to mod their forum - I am, and obviously you are, but some people seem to be afraid of code (of course, the extension system in 1.3 should change things quite a bit).

I was speaking of a mostly stock install of each, but of course you're right (though please remember that I never said that PunBB could not be used for such a purpose, just that it might not be the best choice - although that is purely a matter of opinion), with significant modding, PunBB could be an extremely feature-rich forum app to rival vBulletin (but along the same lines, I could also say that with "significant modding" a piece of simple guestbook software from the 90s could be made into feature-rich forum software, could I not? )

i hope this one gets converted to run with PunBB 1.3.

1, 3, 4, 5, and 6 all the way!

As for 2, I don't have experience modding other forum packages, so I really couldn't give an honest opinion.