Star Wars: The Old Republic Has 73,725 Guilds Currently Registered
If you haven't yet registered your guild for Star Wars: The Old Republic, you are officially late to the party. You might want to get on that as many of the names you might like are probably already taken. Or if starting a guild isn't for you, you will more than likely find one that fits you out of the 73,725 registered guilds. According to the SWTOR guild page, the guilds are split 60:40 in favor of the Empire.
The Empire currently has 41,738 registered guilds, or roughly 60% of the total. The Republic only has 31,987 registered guilds.
Granted, the majority of these guilds only have 1-5 members currently in them, but it's still an impressive number considering the game hasn't released yet. This number should continue to grow up until launch, but I expect it will retract slightly as guilds merge and some of the lesser populated guilds die off. What tends to happen is members of the smaller guilds merge with larger, established ones in order to perform raids, or Flashpoints/Operations as they are called in Star Wars: The Old Republic.
The page breaks the registered guilds by server as well. There are 29,387 guilds registered for PVP servers, 32,551 for PVE, and 11,787 for Role Playing.
On a side note, if you were planning on naming your guild after the popular Star Wars spoof, Spaceballs, you're out of luck. There are currentnly 68 registered guilds with some form of the name in their title. The most popular being Spaceballs The Guild.
Have you picked your allegience yet? You wouldn't want to travel to the Voidstar alone, would you?