I'm giving a presentation in about a month and I'm planning to use Keynote on my Macbook Pro. I was hoping to use the iPhone Keynote Remote app, to act as a very modern version of a slide changer (if that's what you call it?). Keynote Remote expects both the host computer and the iPhone to be on the same network; but there are numerous reports of connection problems between both, not to mention the fact that you don't always have a Wifi network available at presentation venues.
Then, I had the bright idea of using the ability of Mac OS X to create an ad-hoc wireless network by clicking the Airport icon in the menu bar and clicking "Create Network...". When I tried to connect the iPhone to the new network (Settings/Wifi) it appeared to connect - but the menubar network icon still showed a worse than Edge connection (I get terrible reception here). Keynote Remote would work for a few slides, but then the connection would drop out - making it useless.
After the usual Googling, I stumbled across this Apple thread which suggested turning Airplane mode on in Settings, and THEN connecting to the ad-hoc network. For some reason the iPhone now shows a Wifi connection and Keynote Remote seems to be working reliably. Excellent tip!