The spider guard is a position we see with the gi much more often than no gi. Amongst a lot of the higher level athletes, a good open/spider guard is what makes their guard seem un-passable. Michael Langhi, Cobrinha, most of the lightweight atos guys, etc. are great examples of what this type of guard can truly become.
Here is a video of some important principles as well as sweeps from the famous Caio Terra