I did a few jobs as a freelancer on elance.com and made just over $800US. How do I include this in my income taxes? Casual income? How do I tackle US$ to CAD$ conversion?

I don't have my own business and don't necessarily see the sense in claiming this as "self-employment". But do I have to?
Elance.com charges service fees. Are these my expenses?
When I do the US$ to CAD$ conversion, do I use the date of the transaction/payment to find the rate?