Activision is also offering a complete refund of your purchase price for those of you who don't want a replacement disc.  You'll have to send back the guitar controller, guitar strap, and of course the game in its orginal packaging. Activision would like you to send it via UPS 3-day. Find what you need on the Guitar Hero III Wii Refund page. 

Now about that replacement disc... Do you want the good news first?  The good news - Activision is indeed sending out the fulfillment forms to those of you who have registered to trade in your mono GH3 disc for those with the promised Dolby Pro Logic Surround Sound.  The bad news - you will be without a GH3 dsic for 3 or 4 weeks after you send in your mono disc!  via Kotaku

Ok all you GH3 fans having to suffer with mono sound -- word is out that replacement discs should (which of course means that they might not) be shipping next month. For those of you who have not registered for a replacement disc, you can register here: http://www.activisiongameexchange.com/. Just fill out the form and click "submit." Much easier than playing a riff on Hard for some of us! 

If you are looking for a skin for your GH3 Wii guitar, check out the 74 skins available at DecalGirl.  Here's the link: http://www.decalgirl.com/browse.cfm?viewfrom=49&catid=265&step=2.  Each skin comes with a matching skin for the WiiMote!