BitBucket is a vital part of Atlassian's internal development process, all product teams use it on a daily basis and we treat it as a mission critical service, I'm really surprised by this comment as here in Sydney we rarely see any issues, I would be lying if some hiccups hadn't happened in the past but they were usually in very short duration, and usually only affect the UI so you can still pull/push using HTTP/SSH, moreover we have a 24/7 dedicated team to respond to any outages and there is absolutely no differences in terms of infra-structure of free vs. paid accounts inside Bitbucket, so rest assured that we put a lot of effort on making the site better for everyone.
We would love to hear more feedbacks like this through our usual support channels when it happens so we can investigate and improve our service.
(Disclosure: I work on Atlassian's OnDemand team).
We improved the architecture a few months ago and that should also contribute to the stability of the system as a whole, see more at: http://blog.bitbucket.org/2012/08/24/segregating-services/
And you can follow the status of the service at: http://status.bitbucket.org
We would love to hear more feedbacks like this through our usual support channels when it happens so we can investigate and improve our service. (Disclosure: I work on Atlassian's OnDemand team).