It's not solved. Here is the workaround that will make Skype work reliably until this little sound bug is fixed:
0) (I'm adding this "step-0" just in case you have a problem installing it from the "software manager")
My Mint8 Software Manager did not allow me to install skype after a complete reinstall (had a yellow check box to the left of it), I went to the skype website to download and install it skype com/download/skype/linux/choose/ selecting "Debian Lenny" and then install.
Launch Skype, click on the little blue "S" icon in the bottom left, selected Options (or just press Ctrl+O in skype), in the list it presents you, go to Sound Devices, un-check the box labelled "allow skype to automatically adjust my mixer levels". After this, go to step 2 (even if you have already done step-2: because if you tried to make a call after that, the setting will have been reset by Skype).
Now, adjust the microphone input volume to amplified (approx.) +75% past the unamplified mark (or 175% of level-1 non-amplified if you're a mathematician), using the "Sound" item that is in the Mint Favorites Menu by default (click on "Input" tab, then slide the slider 3/4 to the right).
If you use your computer's speakers, at this level, it will probably send your caller's voice back into the mic, giving them an echo. You can play around with this slider until you find a satisfactory level for your mic and your caller, sliding it between +60 and +90% range, I'd expect. Of course, if you use a headset, you won't have the feeding-back sound echo problem.