I think that the main problem with abbreviations is that not all the people abbreviates on the same way, so when you work with many people it only can increase the probability of error when coding. For example if you have a constant that can be called SOMETHING_INTERFACE, maybe some developers would abbreviate it as SOMETHING_INTFACE, others as SOMETHING_IFACE or SOMETHING_IF, SMTHING_IFACE...
With only two words you can have at least half a dozen of more or less "logic" possible abbreviations, so I think it's better in the most of the cases to write without abbreviations and with more reasons if you want to have self-docummented code.
Very long names can be annoying sometimes, but can also be abbreviated in very local scopes using auxiliar variables.
