Me, now (well, the far south of Tunisia & Egypt next week. Then Jordan & Syria).
Very hot, and pistes being covered by moving dunes can turn easy routes into complete hell - have to ask / wait for others returning to know. Have also been caught in a sandstorm in the Chott El Djerid (no shelter) which was a nightmare, making my face really sore even with a cheche and stripping stickers off my tank...
Agree about more strain on bike!
The instant you stop you have to take off clothes, and you become instantly soaked in sweat. Simple digging becomes exhausting and sometimes you cannot drink enough.
Driving from 0700-1100 and 1500 until dark is not so bad, but the right clothing is vital (I have SixSixOne armour vest, CoolMax shirt, MX lid, light gloves, Hein Gericke tuareg shorts, knee braces and MX boots, and a cheche for my neck).
Getting stuck and ending up in featureless desert in the middle of the day is no fun, and you would be surprised, even if you are well-prepared, how hard it is - like someone said, there is just no shade / respite AT ALL. Scary.
I have the 3L CamelBak MULE bag. As well as the water I carry a Sigg bottle of rehydration solution and my medkit all the time (and some dates and baclava sweets). I have to fill the water up twice per day, just from riding.
For the bike, 20-50 oil and an oil cooler. Try not to work it too hard. Remember that air-cooled bikes radiate heat onto your legs, and stop you from cooling down as much, especially when you are standing & gripping the seat / tank with your legs.
I keep getting vapour locks in my fuel filter, even though it is as far from the engine as I could get it. Wrapping it in foil helps, but even so, I have to squirt mine with the CamelBak sometimes
There is nobody on the pistes, which is wonderful, but a bit more dangerous. If you can (like here in Tn), check out and in with authorities at either end of the piste. Even local people often avoid travelling in the summer!
If you ever find youself thinking "it will be OK" you have to STOP and check again!
HTH - probably more tips as I find out the hard way in the coming months!