There have been several threads about creating a standard for the nomenclature to describe fractions of Bitcoins, using names, the metric system, colors, etc...
What if the client simply used updated exchange rates? Let's say I want to send money to my buddy in Euros. The client can simply download the latest exchange rate off of Mt.Gox (or Tradehill or whomever), the user can enter the amount in Euros, and hit send. Even if it comes out to 0.0035982BTC, it would be completely transparent to the user.
Maybe 10-15 years from now, Bitcoins will be able to stand on their own (or not), but until that happens, why not have the client use conventional currencies alongside the Bitcoin value?
I think that's way more misleading. You'd be sending btc, but you'd be presented with the btc amount translated to another currency? Confusing. While I agree that lots of people are too thick to not be turned off by decimal places, the solution is just to start using mBTC or Bitcents or something as the unit most commonly referred to.
You do NOT want people always thinking in terms of some other currency. You want them to intuit btc (or mBTC, etc). Yes, that will take some time, but it's what has to happen for reasonably widespread adoption, and it won't take THAT long if there are enough bitcoin merchants out there. Ever spend any time in a foreign country? After a week or two, did you still convert everything in your mind to your native currency, or had you gotten used to it?