Currently running 11.10, 11.04 and 10.10 depending on which machine I'm using. Servers all on 10.04.
LibreOffice is a new version of OpenOffice. In a nutshell the developers of OO had a row with Oracle (the company which 'owned' OO) and left en-masse to start LO. LO is now developing much faster than OO used to, so generally 'a very good thing'. Libre should have just taken over all the OO stuff 'transparently'.
The new interface (called Unity) takes some getting used to. It's still very young so it will improve very quickly over the next year or two. It's taken me ages to get comfortable with it - but I'm OK with it now. In a year or so I think they'll have a world beater on their hands.