Unfortunately, multiple wallets is somewhat inevitable, and although bitcoin tries to hide the mechanics of all the key management, I think address management is a huge risk. People have a natural tendancy to use the last-known-good address and wait for something to go wrong. I'm sure we all know people who would write one bitcoin address down once, and expect it to always work. That's a really dangerous expectation. By this point, I've installed the client on 4 different machines several times, and although I don't need all of those addresses .. if it's out there .. there's a risk someone will use it.
OK, I need a bit of clarification here. My setup is as follows. I have my day to day PC, which is also my mining PC. On that PC I have Bitcoin installed and my mining proceeds get sent into that wallet.
I've also setup Ubuntu on a USB stick. It's not installed on there, it just runs, so it's fresh each time it boots. On another USB stick I have a copy of the Bitcoin install program, a copy of the TrueCrypt install program, and a copy of the Wuala install program. What I've done is, last night, booted the Ubuntu stick, installed the above programs and created a new wallet. I didn't generate any other keys other than the initial one. I took that key and emailed it to myself.
On my main PC, I transferred 0.5BTC to this new address (the Ubuntu address). On the Ubuntu stick I downloaded the entire blockchain and verified that the transaction showed up. At that point I created a TrueCrypt volume on a second USB stick and moved the wallet.dat file into that encrypted volume. I also zipped the wallet.dat with -e and uploaded it to Wuala (as a backup backup). Wuala encrypts all data anyway, but I figured it didn't hurt to zip encrypt it as well
As the blockchain took bloody forever to download, I also made a copy of that on a separate USB stick.
I then shut down Ubuntu, and restarted it, verifying that everything was gone and fresh, then went through the steps of reinstalling all the above programs and recovering my wallet.dat. All good, all blocks present, along with the 0.5BTC.
Satisfied that it all worked, I then transferred the total remainder of my BTC from my main PC wallet to this Ubuntu "savings" wallet using the initial address I'd emailed to myself.
Booted Ubuntu, and again verified everything was present, then made a final backup of this wallet into TrueCrypt and Wuala.
So now, whenever I accumulate some BTC on my main PC from mining, I'll just send it to this Savings address (I won't bother checking it worked from now on, other than looking on Block Explorer).
My question, after than long winded blah, is to your point above about only using that one address. What are the risks/pitfalls of doing that? If I only ever send my BTC to that one address (which is pointing to a wallet that is encrypted on a disk and only accessed via a LiveCD when I want to spend it), is that a problem? No-one can do anything with that address, not unless they get through all my crap and get my wallet.dat right? So why is it better to have multiple addresses?