I believe there's some sort of licensing thing that lets LibreOffice do what OpenOffice cannot. LibreOffice reportedly has more features these days versus OpenOffice. Your easiest bet for determining the difference is going to be swinging over to YouTube and watching a demonstration to help you decide.
Note that today, LibreOffice tends to be the current standard on most Linux distributions. I just got done installing the LibreOffice suite on my new Linux machine, in fact. I cannot tell you what is and what is not compatible between LO and MO documents at the moment, but a friend of mine on another forum switched to LibreOffice and is very happy with it for producing media. I did use the LO equivalent of Excel the other day for running some numbers, and did not note any difference in procedure as compared to Excel.
...In general, you are getting an office suite. Think back to earlier days, when you may have had a computer that came with Microsoft Works. Was Works that bad in comparison to Word for the average user? Probably not. It even came with a kick-ass dictionary that I really wish I could rip out of that old Vista machine and port to my other computers! I would not expect a seamless transition between MS and GPL 2 or 3 software, but I don't anticipate it will slow you down as a whole. Again, it's an office suite, and whatever you choose is probably going to be fine.