I know Greater Mage Hand lets you carry stuff up to 40lbs with it, but is that useful in combat, or just more meant for roleplay/story segments?
One of the great beauties of role playing is that you use your imagination to solve problems the dungeon master throws at you (in some cases the problems may be ones that you yourself created). Like a 10' pole, I think Mage hand could definitely be used for a lot of different scenarios including combat.
Perhaps an Orc king is disarmed by the fighter and you the Awesome Mage decides to use Mage hand to move the orcs blade away so he can't pick it back up, rendering him extremely ineffective in combat (he may even surrender). That could be very useful in a combat scenario.
I'm not going to make a list of answers but a Mage hand could be more useful then a fireball in some situations.
Honestly the usefulness of certain spells and pieces of equipment are only limited by your imagination and I think Mage hand, like the 10' pole is one of those things.
I'd call it a highly situational combat spell, and not up to the standards set by heavy-duty 1st-level combat spells like Grease, Sleep, Color Spray, Power Word: Pain, Enlarge Person, and so on. If you have a limited number of spell slots and/or spells known (which is more or less always), I can't imagine myself picking this spell for reasons of it being mechanically good in combat on its own.
It's likely to be more useful, relatively speaking, if you find yourself frequently fighting armed humanoids with bad Will saves (such as low-level NPC Warriors), as the spell can be used to disarm, probably its greatest combat use.
It doesn't reach far enough or lift heavy enough to use it to deal damage by dropping objects. Most characters fall outside the weight limit, especially once gear is factored in.
It is one of those spells where sufficient creativity coupled with DM leniency could result in something fun happening, but my verdict on its mechanical viability in combat is definitely "mediocre" at best.
To augment the other answers, here's an (extremely incomplete) list of things that you can do with a Greater Mage Hand:
The best uses of Greater Mage Hand depend on interacting with things, so its value depends on what other things there are for you to interact with, including what you have in your pockets. Pot of boiling oil sitting over your enemies, with a small lever to tip it? Perfect. Featureless plain populated by golems? Useless.