Hi Xordan,
First of all welcome to the PS community!
Actually that is the first point as well. PS is a communitty that works together to build the idea and support the Development team in creating the game of Planeshift. In being a community one naturally tend to get to know some ppl better than others and also one gets on better with some than others. Guilds are a natural way to band together ppl with the same interests and personality types.
Also there are so many aspects to a fantasy world such as that created in PS. One could never be involved, and probably won\'t be interested, in all of them. That is where many guilds come in. Some are interested in fighting skills, others in magic or being rogues. Some just want power and therefore band together. Others again are taken up by the issue of being good/neutral/evil. So depending on where your interests lie you will probably be able to find a guild(s) of ppl that share that interest.
In the game itself guilds will play an important role with issues such as guild wars being programmed into the game. By it\'s very nature guilds will also have a big influence on the game as many players bound together in a guild will tend to go after the same objectives thus multiplying their effect.
In my own experience having joined and becoming active in a guild has really brought the PS experience to life. I\'ve made some really great friends and we have a ball together on-line in our own guild-forum, here on PS forums, on our own IRC channel and so on. We have even started role-playing on our IRC channel now since there is not much to do in-game in PS until the next version comes out.
Of course one can just choose to be a loner and not belong anywhere. There are some wo do so and will choose to play like that in the game too. In the end it depends on your interests.
Good luck.