If you want to save a large amount, it's no problem to wait.
If you want to spend a smaller amount, it's no problem to land them in instawallet between where buying and spending.
If you are making a big purchase, get an address from the person/business and buy right to that address.
This is a problem with many solutions.
It does not sound simple to newbies.
If we properly explain to a newbie what to expect, there will be no worries or disapointements. If you want to run your own bank, you'll need a full client, which initially takes a few days to prepare itself. Once this is done, it will quietly run in the background, and you can use it whenever you need to. Alternatively, you can use one of the "light" clients or Web services, which rely on third-party servers, but you still keep and control your bitcoins on your local machine (bitcoin spinner, blockchain.info, etc.). Finally, you can keep your coins with a third party (online wallets, exchanges).
