.So I have read this forum and I don't think anyone has suggested this, if so I apologize. Anyway, I have an HTC inspire and this is the only phone I have tested this on. I figured out how to make the shutter sound for screenshots as loud or quiet as I like. This is what I did. I have my notification volume set to the same volume as my ringtone first of all. Also I have downloaded from play store an app called Android Assistant. In Android Assistant you click tools on the top right then click on the volume control section. In there you can adjust whatever volumes you want. I believe the shutter sound is linked to the notification volume so I can just put my phone on vibrate and it did work as well. Remember to set your notification volume to be the same as the ringtone volume in settings. I have tested this so I hope it helps everyone.
Thanks,
Jeremy
Edit: I forgot to mention that if you have the notification volume set to the same as ringtone volume then you should be able to use the softkeys on the side of your phone to set to silent or vibrate and that should do just as well. Sorry for the confusion.