Facebook in my opinion will win the battle , its shear reach and global acceptance ratio while maintaining a extremely small engineering staff ratio make it faster and more innovative , less bureaucratic and technically agile. Size is difficult to manage when everybody is so smart , digital armies in my opinion are like Spartan warriors , easier to manage in smaller regiments .
Additionally Facebook is gaining less enemies as it grows and is not intruding as much on the Revenue turf of other companies , consequently i think this will permit it to grow for a longer period of time with less competition as their is less need to compete with extremely well capitalized users
Below is a very interesting post about www.facebook.com from inside
