Disclaimer: I use Ubuntu for development and Ubuntu (server) for production servers. I might be a bit biased but it seems like you're looking for somebody who's actually gone down the same path as you.
That out the way, I love using Linux for development. Most of the tools I required are the same: Eclipse for PHP/Python and a souped-up text editor (gedit in my case now, was Dreamweaver's text mode) for HTML/etc. Under Windows I was limited to FTP* which stunted my workflow a little. Under Ubuntu, I can just mount the working directory and work straight from it, or use a version control app like svn, git or bzr.
Lets get one thing straight: you will spend more time on the command line but I don't see that as a neccessarily bad thing. I have short alias commands that do a million times more than five minutes clicking around several Windows windows could accomplish. If you have Linux servers, chances are you do a fair portion of your administration over SSH already, so it shouldn't be too much more of a jump.
But even just on the desktop, there is a modest learning curve. The initial annoyances mainly come from finding the "right" applications. There is a lot of choice and very rarely do you find a direct mapping to a Windows-only app. This just takes some getting over. You will get used to something provided it's functional and you actually use it. That's technology for you.
For stuff you just can't drop (Adobe Fireworks and Photoshop for me) you can use Wine to "emulate" Windows (though it's not really emulation) or use a virtual machine like VirtualBox to run a real copy of Windows in the background. I only need these apps for 10-30 minutes at a time so I just fire up a TinyXP image in VirtualBox. Your mileage will vary with both alternatives.
Pros of Linux:
- Free (in both ways)
- Plenty of dev apps
- You can make it mirror your production environment (cutting out nasty surprises)
- Generally well supported with updates
- Looks gorgeous if you put enough time into using the right effects =)
- It makes you much cooler. Fact.
Pros of Windows:
- You've already got it so you're not going to have to spend a week reacclimatising
- You've already put money into it
- Upgrades do a very good job of clearing out your wallet of all that troublesome cash.
Ultimately, it's really up to your personal work-flow and tastes. Both systems are more than capable or providing a decent work flow.
*I wasn't limited to FTP as such but getting a svn (or other) server set up back then was, I'm ashamed to say, beyond me. But Windows would not support my current configuration which relies on bzr+ssh... So perhaps it is Limited. I'm rambling.