Is it possible to copy a wallet.dat file from one computer to another and access the same wallet in two places? For instance, on a home PC and a work PC?
Possible, yes. Recommended, no. The wallet contains unused keys that are pregenerated. Whenever you use one of these, a new one is generated and added to the end. After you get past the shared pregenerated keys, the wallets will diverge and things can get messy.