Before running the setscene tasks, BitBake runs through a process of checking which sstate packages are available. If you have SSTATE_MIRRORS pointing to some remote server on a slow link this process can take significant amount of time and there's no message or other indication as to what is happening. According to Richard this functionality is in sstate.bbclass in sstate_checkhashes() iterating over fetcher.checkstatus(). We may need to send some events (bb.event.MetadataEvent ?) that the UI can pick up and report.
Fixes merged to master: http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=8d56d596bb2e48332e8f8c6aed78445f7ffb44bf http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=e769dce794a4724e1bcfdd61652ec54d9520c29f