This has got me thinking. When transactions occur the coins get "broken up" if needed to make the payment with some change sent back to you. Wouldn't that mean that slowly the coins will get broken up smaller and smaller with time causing the kb for the transaction to go up, making the data required for transactions to slowly go up?
They tend to get put back together when you send larger payments.
The algorithm that the current bitcoin client uses isn't the best possible algorithm for deciding when to combine or split coins; ideally, it would have some notion of how big your average transaction would be, and when sending coins it might split change or combine extra coins to make change that is about that big (so the next time you make a transaction there are old, previous, high-priority transactions it can use).
If you ask nicely, I bet tcatm or somebody else will create a little web service that could tell you how long you have to wait for a 0.10 (or whatever) coin to mature before you can send it without a fee.