we traveled over the Salar a few years back. It was then quite obvious where to travel as there are many dark tracks left by the many landrovers and jeeps that 'bomb' around the Salt pans with tourists coming from La Paz etc.
If you stick to these you should be OK but it is also very wise to have a GPS and some ref points. These are all over the web (I would give you ours...but we lost this track log!) and probably here in HU too. One hazard to look out for are the Ojos del sal.....'salt eyes'....holes in the salt that can come up where you dont expect them - so just keep your eyes open!
You can get fuel easliy in San Juan - a small village just before the Salar de Uyuni - (usually you have to ask someone and they will point you in the right direction usually someones 'house' and he will then fill you up out of a fuel drum/cannister) there are a few hostels there - we ended up staying at 'Alojamiento Lipena'. hot showers too! . Contact details for ‘Alojamiento Lipeña’: tel -0261 37232. Cell – 72431289. GPS - S20 54.048 W67 45.990. They offer single, double and group rooms and have space for 30 people.
In Uyuni itself there are many places to stay and gas is easy to come by -we stayed at Hotel Avenida -they also had a courtyard area where we were allowed to place our bikes, right by our room…great! But in our opinion the town of Uyuni is a dissapointment.
there are a few different ways to approach the salar....one not so easy (which is the one we chose!) and another which a lot of the jeeps take so one of the main problems here are corrugations.
if you want to have a read of this part of our trip at:
2ridetheworld.com : diary
enjoy the Salar - its quite a amazing place - and dont worry, I rode across the salar with a fully laden (320kg) motorbike...and me a mere woman! so no -probs!
BTW - it is always a good idea to carry with you a good map of the country/area you are going through PLUS GPS!
Bottom line is - be prepared but it is not the extreme ride that perhaps your friend is suggesting.........