Really used from 1997-1999 and then again from 2003-2005. Used sparingly for basic text editing on both classic and OS X, never very seriously; by the time I was a Serious Programmer on the Mac I was using TextMate or Vim.
Used Pico on Linux or Unix distros which weren't sufficiently ra-ra about Free Software that they gave you Nano instead. Eventually learned enough vi(m) to give up the habit, thankfully.
vim is, well, an improvement, but knowing vim means vi is as easy as remembering not to try and use (insert everything useful here) when stuck on a shitty computer that only has vi. Which is thankfully rare these days.
Used Nano on Linux distros which were strict GNU followers, e.g. Debian. At least, until I was able to muddle my way around vi(m). Thankfully that only took a short while...
The One True Editor (unless you are an emacs heathen -- not that there's anything wrong with that...)
Could write reams of text about why it's so awesome but this isn't a review site (you may be forgiven for thinking as much if you see my other entries).
Had a brief dalliance with Gedit in school while using Gnome personally, or on occasion when on computer-lab systems that only had Gnome available. It's okay.
Before I became a full-time OS X geek, I preferred KDE for Linux desktoppery, and Kate was a very passable editor that happened to be built-in to it. I can only imagine it's even better now 5 years later.
Probably the best GUI text editor out there, save for files larger than about 100k.
Once I got better at Vim (and found Vim's column selection/tabs/etc) I ditched TM and made Vim my sole editor of choice.
