Some times I wonder "Why Open Source?" and think how would I explain something that is almost second nature to me to someone else. I think I've worked out the answer: its about finding the best solution. But what is the best solution?
The best solution is an interesting question that I don't think can be always definitively answered - you need to work it out case by case. For example I use Joomla! a lot for a few websites I run and I also work on the project. You'd think that I'd tend to use Joomla! everywhere for every problem but realistically that isn't the power of open source.
I run Wordpress for my blog because at the time and even now it offers a great blogging platform. I wouldn't try to make much more of it but for the simple stuff that I'm trying to do with Wordpress it works just fine. My blogs get posted, the search engines get pinged and I have comments that work fine and are spam protected via Akismet. What more could I ask for? For this particular task (blogging or very light and simple content management) it does the trick. When I need something more complicated or detailed I switch to Joomla!.
Then there is TaskFreak. TaskFreak is a really awesome application that I use to keep track of my long term tasks. Unfortunately the list is slowly getting longer as more and more stuff gets added to it however thats not its problem and it does a great job of data entry, editing and keeping stuff out of my way. Its one of my favourite tools and it just works which makes me happy. It is kept out of the public eye a bit since I use it more for personal stuff but I can really recommend it.
Mediawiki is perhaps one of the best known tools as the engine that drives Wikipedia. Whilst most users probably don't know or care about it, MW is for me a brilliant wiki tool that fits my needs perfectly. Not everything easily fits into Joomla!'s more rigid content model and nor does it always have to, so in some cases for documentation that should be more free form I prefer to use Mediawiki.
And just today I've deployed "SIT!" which is an interesting application. It isn't doing the greatest at the moment as the application was a bit of bother to install. But here in lies the beauty of open source, you can take the thing apart and look for the problem to find it. Not only that but you have stuff like public bug trackers where I found exactly the issues I was having and their solution in a single spot. There was one issue however that didn't have a solution so the coder in me dug through the code and fixed it quickly and raised a new bug report.
But I think at the end of the day is that ability to find a tool that suits your needs and deploy it for free, evaluate it and potentially work through any issues with a bit of knowledge and more options than closed source/proprietary before you have to commit to buying it. I'm not against paying for software, I have some brilliant tools that make my life easy that aren't open source and aren't free, however before I resorted to them I evaluated the open source and free tools easily and quickly.
And at the end of the day what you need is best of breed applications - and sometimes being free doesn't hurt either.