Bitcoin Forum

So I'm wondering if the bitcoin client needs to be open when you do a transaction ?

If not how often do you need to open it if you just have a wallet that receives funds for "safe keeping"

No client does not need to be open for receiving transactions.

You do not have to open it for as long as you like. Just make sure that if you make a wallet for backup reasons to generate enough receiving addresses in advance, because if you make new addresses on a running copy that are not in backup they most likely wont show up when you run backup copy.

Has anyone tested this?

I thought wallet.dat was just a key to cash out only and all other data is stored on the global p2p network?
Just when I thought I understood how this works, Now, im confused again.

Exactly. Receiving money is not cashing out, so the data is stored on the global p2p network. You don't need to do anything.

Bitcoins will always remain in the blockchain. To move them you need the "key". Each address has a unique key that allows you to send them. A brand new wallet contains 100 keys. If you all you do is receive and don't create over 100 addresses in the address book feature the wallet will last as long as you want. When you SEND Bitcoins sometimes extra addresses are used up so you'll reach the 100 keys faster. Once the 100 are used up another 100 are made. So backups will last depending on how often you do send transactions or create new addresses in the address book. The more you make the shorter duration you should make your backups. 

Damn, you guys sure know a lot about this!
Is all this info just from the wiki alone?

wiki + board + personal experience + trail and error