I occasionally get asked this by real live people - and also it comes up a lot in places like /r/linux4noobs, so I thought I’d try to provide my answer for this.
What has open source done for me lately?
Open source apps are better, not just cheaper.
Repositories & Package Managers
Freedom to Customize
Don’t like the way your favourite software has changes? no problem - just use an alternative, or keep using the existing one. It’s open source, you can do what you like.
70% of all web servers run linux - it’s cheap, fast secure and well supported. Why not make you development environment match your deployment environment.
Programming == text processing == unix toolbox; tools polished over decades.
All the Cool Kids are doing it.
The native platform of an increasing amount of cool new things is Linux, not Windows. This goes back further than people think - Ruby, Python, Perl, etc…