I recently restored my wallet.dat file from another machine. The wallet.dat came from a Linux machine (debian), and was restored to a Windows bitcoin install.
After restoring I can see the correct bitcoin address, but the balance is 0 BTC. The client is still downloading the block-chain (152,000 blocks at time of writing).
When will the balance show? It should have a balance of 0.66 BTC.
The wallet was restored using the answer from this question: How can I restore my wallet?