OpenOffice is great, but it fails way too often at this task.
LaTeX doesn't do anything to help me figure out what to say.
For word processing, OpenOffice is pretty good. It's biggest failing compared to Word is a lack of a good organizational tool. It has some kind of "navigator" mode that has occasionally been offered as the answer for people who miss Word's outline view, but it doesn't compare. A few years ago, there was a post on the OO developer forums where a major OO developer acknowledged that this was a serious lack, and said it was on the roadmap. However, it would require a lot of chances so we were not to expect it soon. When that gets in, OO will be a lot more useful.
For spreadsheets, the gap is larger, and OO is behind not only at the high end (which is arguably not too critical--most people aren't using anywhere near the full power of Excel) but also has too many annoyances for casual use.
For example, on my gaming PC I wanted to use a spreadsheet to keep track of data on my sales from the auction house in Warhammer Online. When adding the data for a new auction, I needed to enter the date and time into a cell. Surprisingly, OO does not have a good way to enter the current date and time into a cell!
It has a functions that give the current date and time, and you can put those into the cell. That cell will then update to show the current date and time every time you open the spreadsheet or recalculate.
You can have a cell with those, and copy the values and paste the values, not the formula, but that is clumsy and awkward.
The best solution I've seen is to use a formula (such as =NOW()) in the cell, and then turn off AutoCalculate for that cell. That will freeze it unless you explicitly tell it to update. BTW, the manual claims that AutoCalculate does not apply to formulas involving NOW(), but what they mean I think is that the formula does not automatically update every second and trigger an updated of the whole sheet.
In Excel there are commands to insert the date and time in a cell, and they have keyboard shortcuts by default.
This might not seem like a big deal, but it means the OO is frustrating for my simple task of recording my auctions, and Excel would not be. When a program can in theory meet all your needs, but it keeps hitting you with these little annoyances, they add up.
Joel Spolsky wrote a great article about Excel and its competition from when he was on the Excel team. They and the major competitor were racing to get their next versions out. They had both concentrated on adding advanced functions--the kind of things that you'd use if you were a finance guy at a major corporation working on a complicated merger or an IPO or things like that. Things no normal person does.
Before the release, Microsoft did some serious user testing to find out what people ACTUALLY used Excel for. They found that one of the biggest uses was as a simple database for keeping lists of things, and doing simply calculations on those things.
They changed direction for the release. The fancy advanced functions were put on hold, and they concentrated on adding things to make Excel good at handling lists and doing the kind of calculations people actually wanted.
When that version of Excel came out, and the competitor came out with its "hey, you can do your merger or IPO on this!" set of features, Excel took over the market.
The OO people need to do what the Excel people did.