Now that the ad-hoc wireless bug has been fixed it is possible to share wired or 3G connection through wireless. To create a shared connection:
Create an ad-hoc connection:
Click on the connection in Plasma NM window and wait.
This dialog will appear, just fill in the passphrase and click Ok:
Wait some seconds and the ad-hoc AP will be started:
I was able to browse the web using my cell phone. The WirelessSharing connection did not appear when I scanned the neighborhood, I had to write the essid manually. Using my current notebook as gateway I was able to connect my old notebook to the Internet too.