I spent some time this evening playing with Diaspora installation from their source code (from http://github.com/diaspora/diaspora) (for those of you, who have not heard about diaspora read this http://subburama.blogspot.com/2010/09/right-action-at-right-time-or-is-it.html before continuing) and I was successful in getting diaspora up and running on my system in about half hour.
Here is what the diaspora team claims to be implemented in their blog (http://www.joindiaspora.com/2010/09/15/developer-release.html) and I have embedded my comments (in italics) next to each claim
# Share status messages and photos privately and in near real time with your friends through “aspects”. - Does not seem to work
# Friend people across the Internet no matter where Diaspora seed is located. - Does not seem to work
# Manage friends using “aspects” - Works partly (I can move friends between aspects/groups)
# Upload of photos and albums - Creation of albums work and upload of photos does not seem to work (I tried with png and jpg file formats)
# All traffic is signed and encrypted (except photos, for now). - Yeh, looks like they have this
With regard to their source code, I think its pretty neat that they are using good coding practices and using rails 3 and mongoDB, which is the cutting edge.
Diaspora seems to look like a facebook copy except for the colors.
Diaspora also has this feature called Aspects, which is like Groups. Imagine you creating groups on Facebook and adding friends to different groups on facebook (this feature is currently available in facebook).
Diaspora allows sharing of updates only to specific groups. In other words, say you share an update with the group (or per Diaspora, its 'aspect'), only people in that group see that update. I m not sure if facebook has this feature. But if facebook decide to implement this feature, they can do it pretty easily.
Based on my experience in following Diaspora so far and looking at their technology, I think its far from being a facebook killer primarily because there is no compelling reason for the 500 million folks to leave facebook and use Diaspora other than the anti-facebook sentiment wave that's going on now.