I've always been a Microsoft Office user, but after I had to reformat my computer and reinstall everything after a spyware attack, I decided to install OpenOffice instead of MS Office. My brother uses OpenOffice and he says it is fine. Many businesses and government agencies also use OpenOffice because it is compatible with MS Office and, more importantly, it is free whereas MS Office costs money.
I'm a big fan of free software simply because I am a cheapskate. It have no credit card, so I am unable to buy anything over the Internet. This means I love using Open Source Software. Winzip is one example of a costly product that was great. But the free alternative 7-Zip I found is just as good, if not better, yet less expensive. I am a big fan of small, simple, and effective programs.
I only ever used Word and Excel in MS Office (I sometimes used Powerpoint but rarely) and likewise I mainly used Writer and Calc, the respective OpenOffice equivalents. The word processing program Writer was not bad. Even though it didn't have a grammar checker, I wasn't too fussed because the grammar checker in Word was pretty crap anyway. Writer was a fine product. When you type, Writer automatically predicts the words you are typing and displays it. If you press enter, Writer puts that word in. I found this feature annoying at first, but it's not too bad and in the long run, as I get used to it, it may actually increase how quickly I write.
Calc was a disaster. I am a big speadsheet user. I use spreadsheets all the time at university since I am a statistics and economics student. I use spreadsheets to organize my whole life. Every minute of exercise I do, every minute of study I do, every file I make a backup of--everything goes in my spreadsheet. I have a 180kb spreadsheet file that I wanted Calc to handle. The problem was that Calc was just too slow. I entered a number into a cell, and then the whole thing would freeze for maybe 10 seconds or more. I thought at first this slowness was caused by the number of programs I was running the background, but when I installed Excel and tried the same file on Excel, I noticed that the problem definitely was Calc. For some reason Excel is just much faster and much more polished and user-friendly whereas Calc was just frustrating.