Have developed RSI (repetitive strain injury) in my thumb in the last month. Been trying to work out what it was, and initially thought it was from using my trackpad, but I've been using the same laptop for years without ill-effect. Then i noticed i use the same thumb for the N900's switch that turns the screen off and wondered whether that might have something to do with it, given it's quite an unconventional repetitive movement. I guess it could be a combination.
So I thought I would check on the forum to see if anyone else had a similar issue at all, and prove or disprove my theory.
I can't speak to whether it was the cause or not, but I have found the slider more annoying than I originally thought. If it bothers you, try just using the power button (double-tap to lock, tap+swipe to unlock). Also consider how/where you carry your phone, as the actions that you do to take it out and unlock (probably in one motion?) can affect the awkwardness as well.
You use your pinky finger for that? Strong one indeed.. Like those sumo wrestlers 