I have used OpenOffice and Microsoft Office for years. There really is not a lot of comparison from my perspective. Microsoft Office, while definitely overkill for most situations, just can't be beat for ease of use and compatibility with everything produced. You can argue that the new OOXML doesn't touch ODF formats and other format wars, but the simple fact is everybody uses either DOC or PDF. PDF means using Adobe Acrobat reader, and DOC means using MSOffice if you want total compatibility (especially on the macro front). XLS is even more entrenched, having no significant format competition and perfect compatibility. You can play this game with every product in the suite.
That said, I do use OpenOffice/LibreOffice a lot. It is mostly compatible (reads most formats perfectly, but has issues with code/macros) and is cross platform -- a killer feature for me. Moreover, it utilizes open standards which guarantees that if the developers stop working on it, and Oracle kills its version, I don't lose access to my information. Granted, the defacto DOC format is just about as resistant -- given every other product makes sure to conform to that standard too -- but it is nice to see a default format that is, by definition, a standard and not proprietary format. Lastly, 90 percent of all documents (including presentations, spreadsheets, etc.) and their producers don't use a tenth of the power of OpenOffice, let alone MSOffice and it's additional features.
Given all this, and the realities of Microsoft as a business, I still choose Microsoft Office for most of my work. It is more expensive, and it is only useful on my Windows machines, but it is very annoying opening Microsoft-produced documents and either not being able to use them or being limited because that feature is not yet enabled in OpenOffice/LibreOffice. If/when LibreOffice fully supports VBA or its equivalent that is embedded in documents far too regularly, then I will definitely switch permanently to it. Until then, it just doesn't cut it for me on my Windows machines.
I am a long-time (and gray-haired) developer / DBA in a Microsoft-bound (VLP) shop, and have both a MSDN and MAPS subscription, but I use exclusively "non-Microsoft" applications outside of the development and data world. While I am kind of the "open source evangelist" in my company, around 20 percent (15) of the people are using OpenOffice 3.2.1 along side MS-Office, with the blessing and encouragement of my boss, the IT director.
I've used OpenOffice.org for years -- originally as a porting option between my user base's multiple products. MS-Office imports pretty well, but doesn't offer any way to export to others. Now I use it because it is, IMO, a better product for routine business and personal use. Built from the ground up as a unified program, there's no need for all the seemingly redundant applications of the MS-Office suite.
It also doesn't suffer from (as much of) the overly zealous "we know what you're thinking and trying to do" automation -- which just annoys the heck out of me. I seem to spend more time in battle with Word than with the words.
LibreOffice is the spin-off of OOo, and I've got that late beta in service, along with OOo 3.3.0. I will likely migrate over to that, once it goes RTM.