The first 9 years of my education was in a British setting, and so I spelled a lot of words the British way. When I switched to an American school in 2002, I took a lot of that spelling with me. Some words I adapted rather quickly, but others I have been reluctant to change. One such example of the latter is "favo[u]rite", because the British version has all five vowels (maaah).
An cool phenomenon I recently discovered is that my journal shows when I adopted certain words. The word in question is "cancel[l]ed"; a quick search of my journal gives the following:
\$ ./tools -Sd cancelled
\$ ./tools -Sd canceled
A quick glance shows that all the way through 2006 I used the British version, and the in 2007 I abruptedly changed to the American version. The only disrepancy this theory leaves is the single uses of the American version in 2003 and 2005. I guessed, correctly, to be quotes I put in from other people.