The same with me, but I looked at the right of my laptop screen and saw that the sound seems to be a problem with the major updates when there is one.
Nevertheless that being said do I only have no problems with sound as such after the update to ios 6. Everything plays fine and volume is no problem either.
The only problem I have had since installing ios6 is that now no music is playing when someone calls and neither music when a new sms arrives as neither when new emails enter the phone.
All that happened when i tried out the new don´t disturb button in settings.
Before I did tried it out everything kept working fine, but because of my type of job I found this new feature very interesting as people could still make a call en sms and even when I don´t hear one coming in I could later on when possible still see if someone had called and call that person back. The same with the sms thus.
And it did its work sublissimo as I hoped for...
...but with one nasty problem, namely that once I returned the button to its off position so I could hear someone is calling or has send me an sms my Iphone 4S stays in don´t disturb modus operandi, or thus in its on position even when you visually see it standing in its off position.
With me this is the only issue sinde updating my phone. Everything else works super and had no problems whatsover... till I tried out that don´t disturb button and did put it on instead of keeping my fingers off it.
But who would have known what would happen afterwards...
And yes like with all of you guys, nothing seems to restore it to its previous glory just after the update, even after doing a full restore through iTunes and thus a reinstalling of ios 6 by its factory settings and afterwards all my apps again through the iCloud copy of it.