Derisive remark, a neat play on the (by some considered blasphemic) 'Jesus'. Usually said when people do not act the way they should (according to your wishes, that is).
Variants: 'Oh, come on!', 'duh', and (probably) many others.

another empty nodeshell rescued, hurray!

On some Usenet newgroups, the ROT-13 version of the word, "furrfu," is used in place of the plain "sheesh." This is not as common as it used to be.