I just got my commuter for my 4S today and I've also noticed the lock button to be a bit difficult.
Whenever I had this problem on the commuter for my 4 it was usually remedied by taking the case apart and reseating it.. I've already done that once, but I'll try it a few more times before I say it's an issue with the case.
Also, I don't like how the headphone jack cover and 30-pin cover are just that, covers. On the version for the 4 they actually had rubber that inserted into the respective holes. I felt that offers more protection from like dust and would be more likely to keep liquids out if on the off chance the phone got wet (which my 4 did when I accidentally dropped it outside a tent where it sat in the rain for half an hour and it was perfectly fine. The little color changing liquid tabs didn't even change)
Got one last week for my IP4 and it does get better after a few days. Since its kinda recessed a bit be sure to press firmly to eliminate any bounce (which causes a quick screen-on then off).