I have some various mods and such that require something to be placed in the bin folder of Minecraft... but on Linux Ubuntu there is no bin folder. What should I do?
Just create the folder. As of Minecraft 1.6 the actual game no longer uses a bin folder and therefore doesn't create one, but some few mods still use it. Creating it yourself will be no different than if Minecraft created it for you.
If you are uncertain about the basics of modding, I highly recommend 'Magic launcher'.
This applet allows players to mod without fiddling around with META-inf and bin folder/directories and the mods can be turned on and off with the click of a check button.
Inexperienced modders can break thier MC by adding or removing classes without knowing whats going on. Good luck :)