First, I don't actually use OpenOffice (or any other word processor/spreadsheet) in any significant amount, but I still attempt to get my family to use it instead of the MS Works that's installed, and continually try to talk my wife out of buying MS Office or WordPerfect.
So when she says that all of a sudden the spreadsheet is capitalizing the first word of every cell, I figure (correctly) that it's some autocorrect feature and turn it off, and think that it's probably not as common to want that option in a spreadsheet as in a word processor. But I get an idea and open the word processor, find the same feature and turn that option on. When I go back to the spreadsheet, I find that it has been turned back on there also. The word processor and the spreadsheet share AutoCorrect options! Now that's just dumb IMHO.
But that's not all. Even after turning off the "capitalize the first word of every sentence" option, when you retype a cell and leave the cell, the first word gets re-capitalized! I suspected that some autocomplete feature was to blame, and sure enough the help docs on "AutoComplete" confirmed that was the problem (it said that if you entered "Red" in a cell, there is no way to change that cell to "red" until you turn off AutoComplete). I also found that you could select a bunch of cells and lowercase all of them...my SO said she tried that and it didn't work (maybe AutoComplete was interfering there? I didn't check).
All in all, the problems could be worked around with searches in the help docs, but when trying to get something done NOW, it's annoying for a user (and I don't count as a user :) to search through the docs for explanations of strange behaviors.
Update: In contrast, Excel seems to ignore the "Capitalize 1st word of every sentence" option AFAICT, and if you do enter, e.g., "Red" in a cell, it can be edited to "red" even with AutoComplete on.