Thanks for wrapping that up (+1) - a couple of recent topics are missing though, so here are More Common Questions
Why is there no stable sort order for /sites?
See How to order /sites result in a user friendly way to use it in our apps. for comments, discussion and workarounds.
Why is the site creation date not available?
See Can we add a creation_date to the /sites method? for discussion and workarounds.
Are there any high resolution/scalable (SVG) icons or images available?
Right now there are SVG versions available for the non Stack Exchange 2.0 sites only, see the respective question. Others will likely be added over time once the respective communities haven agreed on something (see area51 + logo for more questions regarding this eventually).
Why are the SVG versions not hosted officially and linked via /sites too?
The respective feature-request has not been acknowledged so far by the Stack Exchange team.
For reference and transparency here are links related to questions already included in Common Questions
Why not return a site_key or similar?
See the declined feature-request please add a key fields to stackauth results for a discussion.
How often should I query for new sites?
See the deferred feature-request Why does the API lack (proper) HTTP cache control headers? for a related discussion.
