I've just published a script that selects the source text in the current segment with only one shortcut instead of doing that with the mouse or moving the text cursor up and selecting with Shift and arrows buttons.

Get it from SF.net
Get it from GitHub

This works beautifully, which made me think that it should be a built-in function in OmegaT. So I sat down and implemented it, but it will have to be approved by the actual OmegaT developers before it makes it to the codebase. Fingers crossed...