Yes it is, although it may change in the future if there's a major change like for example addition of encryption which is planned for version 0.4. Keep an eye on the development.
Yes, wallet.dat can be used on OS X, Linux and Windows
mewants, if u were just starting mining, would u use Linuxcoin?
Yes, it's great distro. Unfortunately, administering remotely proved to be somewhat difficult on the v0.2, so I went with windblows