I posted here about how to get LibreOffice 3.30 in Ubuntu 10.04 LTS, but I left out an important step. In order for spell checking to work after having uninstalled OpenOffice.org, you have to make sure that hunspell is installed, along with aspell for word suggestions. You can do this with a package manager like Synaptic or from the terminal:
sudo install hunspell aspell
After that, open LibreOffice Writer and go to Tools -> Options. Click on Language Settings -> Languages and make sure that your language is set for your tasts:
The Default languages for documents selection must have an icon with ABC and a checkmark as shown above. That will indicate the default language used for spell checking.
Next, click on Writing Aids:
Ensure that Hunspell SpellChecker is checked at the top and that the dictionaries in the middle of the window are all checked as above. The rest should suit your taste.
Once I did this, spell checking worked again.