A few years ago the chances of someone recommending open source software for business use would be very small. There were a few applications that could have been used, but you would have ended up with a mix of software and the chances of compatibility problems would be quite high. Over the last 6 or 7 years there seems to have been a major push from some commercial companies to invest in using open source software and to concentrate more on bug fixing rather than just adding features. This has resulted in the software being a lot more stable than it was in the past. When I first started using this kind of software, back in 1999 or so I would be hard pressed to find a useful piece of software that did not crash after using it for a while, the operating system kernel, C library and command line utilities were very stable, but anything with a GUI would have a problem sooner rather than later. Any large application that I tried to compile would either not finish with an error or would crash when I tried to start it up and this included programs like a word processor, web browser and video editor; basically the programs that you would need to be stable.
Fast forward about 6 years and things seemed to have completely changed. The web browser was compiling without any problems and I was running it for so long that the tab bar would always fill up with tabs. I decided to risk trying to compile OpenOffice, even though it seemed like an impossible mission, and to my surprise it finished compiling and would even start up without crashing. I then tried it out with some documents I needed to produce and after a few months it became my main word processing program and it did not seem that interested in crashing. The latest versions of OpenOffice can even open Office 2007 documents and they are constantly adding new features to it.
Another open source application that surprised me was Mozilla Thunderbird. One of my clients had decided to upgrade their mail server along with some of their client machines. When I setup the client machines I decided to use Thunderbird rather than Microsoft Outlook, because I have had some performance problems with Outlook and IMAP servers in the past. Thunderbird seemed to perform quickly when loading the initial folder list and, once the emails were downloaded, the search was lightening fast as well. A year or so after the install, Thunderbird was still going strong without any reported problems, and during that time I have had to recreate the accounts a few times on a couple of the machines that were still running Outlook