GOTO is a traditional conference where there is a divide between those who contribute content - the speakers - and those who consume - the attendees. SAOS is not traditional and completely erases that divide by demanding all attendees to contribute.
The GOTO format is well known: The speaker prepares a talk based on his/her experience and expertise. The attendees flock into a room, sit down and listen for an hour - all facing toward the speaker. The SAOS format is less well known: Nobody prepares content beforehand, but everybody contributes to it during the conference. Session topics are found through brainstorming and agreed upon progressively throughout the day. For sessions attendees flock into a room, sit down and discuss for an hour facing each other.
GOTO is big - lots of people, lot of tracks. SAOS is small - about 50 people, as many tracks as emerge.
GOTO is well publicized. SAOS is invite only.
GOTO focuses on teaching attendees about ideas or technologies that the speakers already know about. SAOS focuses on finding and developing ideas and techniques.
At GOTO the networking happens in the proverbial hallways and at the social events. At SAOS networking happens just as much during the sessions.
It will be interesting to get to go these events almost back-to-back. I expect the two to be very different, but I also expect to learn a lot at both. It is also interesting that GOTO has a fish bowl session on Tuesday. A fish bowl is in the same vain as the open space format used at SAOS. Whether it really works in such a large setting will be interesting to see. And, by the way, in case you are wondering, SAOS is the successor to the Agile Architecture Open Space Conferences I've run the last two years. This time around I've had the good fortune of getting invaluable help from some awesome partners in crime (Nikola Schou-Pedersen, Jeppe Cramon and Jakob Bendsen), and I think the conference will even better this year.