Not everyone, but many people anyhow.
I don't know, if it works on offical servers, but I tested this one successfully on L2-java:
If you wanna climb onto any mountain (works with all kind of mountains), just click rapidly and many times at a high spot it. Do not give up, if it doesn't work - Get some experiance with this exploit and you will see, it is easier, than you thought at your first time. Then, after a few moments of jumping up and down (like in S.A.L.O.M.O.N.'s guide) your charakter will jump up onto the mountain.
If you have been pressed the left mouse button rapidly and often enough, you even can use hills as some kind of ski jumps.
BTW, if you want to get over a little wall or something like that (for example: to fall down to crumatowers floor <- why ever), do the same. But instead of clicking at the highest spot of a mountain, click at the skyline.
Works fine, too - But not that usefull.
Yes, my post seems to be similar to S.A.L.O.M.O.N.'s one, the difference between L2j and offical is quite big. Hope you got the point.
- Berry