A:
This drive is formatted FAT32, so it can be used both for reading and writing with a Mac for most uses. The two limitations are:
1. It cannot accept files larger than 4Gb (which is a limitation of FAT32, so is the same when used on a Windows machine).
2. It will not work with Time Machine, which requires that a drive be in the standard Mac format.
If you want to write files larger than 4Gb to it, you can reformat it to exFAT and it will still be compatible with both Mac and PC (though Windows XP and Vista would require specific Service Packs to be compatible)
If you're only using it with a Mac, you also could reformat it to the standard Mac format.