The new version of Oovium 1.1.3 includes for the first time support for Apple's bluetooth external keyboard. Expressions will now be able to be entered via the external keyboard. This is particularly useful within the GridBub in conjunction with the new "equal tab", which should make Oovium data entry faster than spreadsheets and even rival that of those old accounting calculators with the tape.
However, as of iOS 5.1.1, Apple has exposed shockingly little functionality to the keyboard. There is currently no way to detect arrow keys, the shift key or the command key. So, the arrow keys will not move you around the GridBub. This functionality was only just added to Apple's Numbers and I'm guessing they used private APIs to accomplish it. Hopefully, Apple will give 3rd party developers access to those APIs eventually; when that happens I will of course add support for the arrows and other key combinations ASAP.