Got my BBB a few weeks ago. My first attempt to update and upgrade the stock Ångström failed. I knew that the in memory /tmp is not big enough for "opkg upgrade" to store the downloaded packages. So I added the "-t" switch to write the temp files to another directory.
However, even the BBB eMMC is not big enough. The upgrade failed and probably corrupted the base. Needed to re-flash the eMMC.
Notes to self: Plug in a USB stick and use it as temp storage for "opkg upgrade" next time!!