In Notifications panel right click and there are two options "Copy All" and "Delete All" options.
It seems little bit strange to me to have "Delete All" option. In many tools I use there is "Clear All" option.
I don't know for others, but when I see "Delete All" there is going to be massive change (like deleting all connections) with massive effect.
But clearing log is just some minor not drastic effect, so "Clear All" is more suitable.
P.S. I have marked ticket with "trivial" importance. It is not urgent, maybe even post 1.7.4 official release.
Windows 7 SP1