I use Skype for Linux very successfully on my 64bit Ubuntu 10.04 distribution – it's a great way to call in to the daily scrum at work, for example. Recently update-manager upgraded my Skype to version 18.104.22.168, at which point I stopped hearing notification sounds (e.g. the incoming-call notification, which is pretty handy!). I still got on-screen popup notifications where enabled, and I could still make calls and hear callers, but no notification sounds.
The solution was to go to the
gnome-volume-control, and massively increase the slider for
Alert volume slider. It had been at about 20%, it's now set at about 95%. However, I can once again hear skype notifications – at pretty much the same volume as before. So I don't know what's changed between
gnome-volume-control and Skype: there may have been an update to the volume control that I didn't notice go by, or maybe this version of Skype is more sensitive to that setting. Still, at least that's one more annoyance is off the list.