My main unusual interest:
Serial numbers on Canadian Banknotes. This "obsession" began just after Halloween 1982, and I was fascinated by the sequence of 3 letters in the serial number as it reminded me of Newfoundland license plates (another weird interest I have). Makes me wonder if my obsession to serial numbers on banknotes evolved from an element of my then-addiction to Sesame Street (which isn't even an addiction anymore now that the politically incorrect content is gone) may have been a factor?
Also, I used to obsess over wanting $100 denominations due to a certain 3-letter prefix that I was attached to since 1988, but that prefix, among all prefixes prior to 2004, were recalled by the Bank of Canada due to counterfeiting problems. This happened when the $100 bill was changed to a new design in 2004, and nowadays the $100 bills are not really an obsession anymore.
I still do obsess over not being given a $10 bill in my change in favor of two $5 bills, even if the cashier does have the $10s, but if the most obsessive element of the banknotes - the serial number format - gets altered, my anticipation for $10 bills will be down the toilet (but for the better). I happen to obsess over $10 bills due to being scarce for nearly 20 years, but it seems as if now demand for the $10 bill may be increasing, as purchasing power for the $5 bill is becoming that of the $10 bill. It's possible that $5 billls won't buy much anymore, whereas $10 bills can buy a meal at A&W, McDonald's, or the like. It seems as if all $5 bills can buy nowadays are a coffee and a muffin/donut at Tim Horton's, or a 6-inch sub at Subway. There are still a lot of $5 bills in circulation, but banks in my region don't get new $5 bills much anymore.
And btw, the Canadian banknotes will be getting a major revamp starting in November. The new banknotes will be made of Polymer material, and there won't be as much variety of serial number prefixes eventually, due to the banknotes lasting much longer. This will really take a chunk out of my obsession for sure when the $10 and $5 bills get revamped in 2013.