I downloaded portable open office last year for resume updating purposes and not having a budget to buy windows office program. The features on it are nice and its stable but it uses a fair share of memory.
I dont use a portable version, but I have used OpenOffice for a few years now. I don't do much with office applications, just the occasional text document, and the occasional spreadsheet. Open Office has always worked ok for me, but you are right, it is a little bit of a memory hog. But can't beat the price
The portable will fit on a thumb drive wich I think was more of a stunt than anything else but it still has alot of features on what I've used of it so far.