How does Bitbucket stack up in terms of reliability? Features are sort of irrelevant compared to recurring downtime.
It may not be github's software as much as they are the number 1 git hosting service and therefore they are the biggest target for hackers.
I might be talking out of my ass here but it feels a bit like the argument for using Apple versus MS, i.e. there are no viruses for Macs since they are more secure... until Apple grew in popularity, which then attracted more hackers to write viruses for Apple's OS, which showed that it is was not invulnerable.
I doubt Bitbucket will supplant Github as the goto git hosting service, but if they grow they might be subject to more attacks? Just a thought to consider.
However, for my serious, closed-source projects (that I might want to become products) I use Bitbucket. So far I've experienced no outages.
However, we have moved to bitbucket recently b.c their pricing was better suited for us.
And to echo xauronx, the new UI really is great and pretty much did for my Github envy.
Just turn off the wiki and issue tracker at GitHub, and link to the BitBucket ones in your README or something like that.