OpenOffice.org's biggest installation advantage over LibreOffice is that it comes bundled with the Java Runtime Environment (JRE). Having a JRE installed isn't strictly necessary for either suite, but it enables some features, and the database manager won't run without it. For LibreOffice, that means the additional hassle of downloading and running a separate installer. Then again, the JRE that came bundled with my OpenOffice.org installer wasn't the latest version.
OpenOffice.org offers localized versions of its suite in 25 languages (more, if you include older releases). LibreOffice differs in that it provides a universal program installer but separate downloads for localized online help. The LibreOffice website lists these Help Packs for a whopping 113 languages. In practice, however, only about 54 of them are supported on Windows, and installing them is cumbersome. You not only have to run the separate Help Pack installer, but you must also run a Custom Install of the main suite to activate locales other than English. Still, if multilingual support is important to you, LibreOffice may have an advantage.
Note that while both suites ship their installers as executables, under the hood they are Windows MSI files. That should be good news for enterprise admins who need to install the software on large numbers of PCs -- except that only LibreOffice's MSI file worked properly on Windows 7. Bummer. (The OpenOffice.org MSI worked on Windows XP, so hopefully this is a bug that will be resolved soon.)
Migrating from Microsoft Office Once installed, OpenOffice.org and LibreOffice are similar in far more ways than they differ. The overall menu structure is identical for both products, except where LibreOffice has added features not present in OpenOffice.org. If you're familiar with one, you'll have no trouble with the other.
Fit and finish differ somewhat between the two suites, with icons and other assets swapped out, though they're sized and positioned exactly the same on both. Overall, I thought OpenOffice.org's icons were a little easier for new users to understand, but of course that's all subjective; really, it's a wash.
I had expected Microsoft Office compatibility to be a major area of competition between the two suites, but alas, not much work seems to have been done there. Both suites handle files from Office 2003 and earlier reasonably well, but support for the newer, XML-based file formats is poor for anything but simple documents. XML-based Excel workbooks survive the transition the best, but migrating .docx and .pptx files is sure to be arduous. If anything, OpenOffice.org was slightly more faithful to Word font styles in some test cases, but overall presentation was so lousy it hardly bears mentioning.