Hi!!! I'm thinking of trying Arch , after having used Ubuntu for quite sometime!!

I just want to ask something about backing up installed packages:
In Ubuntu, I could just copy the contents of /var/apt/cache/archives to some safe place, and after a reinstallation, I just copied back the contents in the respective directory of the new installation...and apt could almost always reinstall them without downloading anything. (I sometimes used a GUI tool called AptOnCD to same effect)

My question is, in Arch if I copy the contents of /var/cache/pacman/ and restore them to a new installation, will pacman be able to install them ??
My ISP charges me per MB uploaded/downloaded, so downloading everything everytime is not feasible! also, I tend to experiment and consequently break my sytem very often, so reinstalling is very frequent for me!! :P

For the ubuntu side, this sounds like a perfect situation for apt-cache, assuming you have a second machine that acts as a server that you will not play with and break.

Backing up all the packages should work fine. Actually I think you just need /var/cache/pacman/pkg, there's also a src directory that contains source code for packages as well, but I don't think you necessarily need that.