It only took me a week to pick it up when I got my fixie but that's because I had been practicing on a freewheeling tall bike. Stopping on a tall bike is slightly more inconvenience than it is on a regular bike, hence the motivation to learn. Also, with clips and straps, it's nice to not have to stop. As far as bieng "worth it" it just depends. Once you're good at it it doesn't take any more energy than standing on the ground but I often don't trackstand at the longer lights because it's nice to rest your feet now and then. I think if I'd been trying for 6 months and couldn't do it I'd probably just forget about it. It's not that big of a deal, but it is fun and does help you pick up chicks. (that last part is a lie)

EDIT: Also, as a kid we used to try to stand still on our BMX bikes using the front brake and little bunnyhops. I got damn good at it and could go for several minutes at a time so maybe that's why it came easy on a fixie.