I bought my first bitcoins around Oct/Nov 2011 for $2.3 USD. I'm ready to buy some now but they were around $6 USD on Friday and they're around $6.8 USD now.

I know nothing about finance or currency trading but have heard good things about campbx.com. Should I consider buying on the margin? I'm not even sure what this is but I've heard it's what the smart traders do when the desired commodity is rising in value.

Any book recommendation for those interested in currency trading that includes bitcoins?