I fell in love with fish while watching a video tutorial for Babushka[1]. I immediately switched all of my boxes over to it as the default shell. Switching over decades of bash scripts was tough at first, but I bought into the whole simplified shell philosophy.

But unfortunately I had to abandon fish after a solid month of using it exclusively. Active development seems to have ceased on it. There are a lot of bugs in the code, at least a couple of which make the shell almost completely unusable for me (for example, running fish from screen is problematic). The mailing lists have some activity, but nothing much from developers. At this point it seems like an abandoned project. As an example of the lack of oversight, the main project web site's domain registration lapsed earlier in the year and it is only back thanks to a good Samaritan.

So I switched to zsh. And it has been pretty great. The configuration files are daunting, but it can do pretty much everything that fish can (and a whole lot more), it is under active development, and is backward-compatible with bash.

[1] http://vimeo.com/6782671 (it's about babushka, but he uses fish as the shell)