When I originally took on a TWiki installation in my new job, I was apprehensive. I wasn't a fan of perl, and I was suspicious about a project that had its own home-grown unit testing framework and build system.
12 months later I am contributing to Foswiki and I can really see major benefits in using it as our application platform, instead of building yet-another-custom-webapp that has a developer, support and security team limited to our own organisation.
Instead we are trying to see what we can bolt on to Foswiki as useful extensions that we should be able to contribute back to foswiki.org where they have the potential to get improvements and support beyond our own efforts.
Our users have noticed a constant stream of updates coming from the Foswiki community: from the WYSIWYG editor they use every day, to the jquery/ajax update of ImageGalleryPlugin, not to mention browser-side page-load performance improvements to NatSkin - for example.
As a newcomer to the project I have been surprised at how easy it is to pick it up and "just do it" when it comes to bugfixing and feature development.
We are really happy that Foswiki has an open and pragmatic process for planning and accepting feature proposals.
We can feel confident that the community process means that decisions will be made in the best interests of the product and its users.
And of course, it's the product that has brought everybody to Foswiki in the first place - structured wiki applications are a really powerful way to get your business done: http://foswiki.org/Support/WhatIsStructuredDataInFoswiki