In terms of added functionality, perhaps the addition of alternative currency rate sources could be explored. For example, other applications use sources like the IMF or the Bank of Canada. I think that the available currencies using the ECB source will be adequate for most people (it is for me), but perhaps offering an alternative may improve coverage for users who need a currency not covered by ECB. Also, you should consider adding some very basic conversions for situations a traveler may encounter: for example, basic imperial to metric measurement, clothing/shoe size, and temperature. I do realize that other applications exist for measurement conversion, but it would be nice to have the basic conversions a traveler would need all in a single application--if simplicity can be maintained. Again, the beauty of your application is its simplicity--if additional conversion capability introduces too much bloat, then it may not be worth it.