Desktops are less expensive, upgradeable, more powerful, and quieter. And you can setup a more ergonomic work area than with a laptop (unless you like a lot of peripherals hanging off your laptop, which kind of defeats the purpose).
If you must work from a coffee shop, just bring your $300 netbook and ssh into your desktop. Why bring a noisy and hot laptop that only lasts for 4 hours when you can have a silent machine that lasts for 14?
Desktops are great for power. Netbooks are great for portability. Laptops are bad at both.
My MacBook Pro is able to do everything I need and I have no problem carrying it around. I think "bad" is a bit of an exaggeration.
Desktops are optimized for power at the cost of obliterating portability. Netbooks are optimized for portability at the cost of being fairly underpowered. A good laptop is a generalist that doesn't do either as well as the specialist but can fill either role competently in most cases.
My major bugbear, I guess, is that a netbook has a crummy, tiny screen. I can live fairly happily without dual head for coding, but I find netbooks' screen/keyboard/slowness unbearable.
My laptop has enough power for my day to day needs (running web browsers, dev IDE, mail, and not taking forever to compile large tex docs), and for my larger needs, well, I need a 32GB RAM server for those, so I wouldn't have a desktop that could handle them either :-). Unless I'm really caning it, it doesn't make a sound, and all I have to do to turn it into a workstation is plug in a USB hub and monitor - not exactly a chore.
In terms of portability, my macbook is light enough for me to easily carry around, and in practise I get around 5-6 hours battery life even after a year's usage. If I upgraded to a newer macbook (I have one with a removable battery), I'd get closer to 10.
I completely agree about not buying a bad laptop. I have no interest in lugging around a behemoth that gets two hours battery life, or one that trades weight for being too slow for my everyday needs. A good laptop (and I'm not just talking about macs here, although I've had extremely positive experiences with mine) is powerful, light, and has good battery life. Unfortunately, you have to pay extra for that, but considering it's my only work-related expense, it seems cheap at the price. I love not being tied to my desk.
I've never noticed, as I use xmonad and don't really worry about screen real-estate. I started using a Windows 7 netbook, and you're right, the tiny screen makes things difficult. The solution is to not use Windows :)
I've never used windows on a netbook. My eyes aren't so great, so I tend to run slightly larger fonts than most people would, and the amount of information I can get on screen at once just isn't reasonable. I can't imagine trying to use Eclipse (say) on it.
In general, I just wouldn't consider a netbook suitable for doing a day's coding on - it's great for short term use, or if all I need is a couple of terminals, but it just doesn't have enough power or usability. That said, if it works for you, then great! I imagine it probably comes down to how much time you spend at your desk - if you're largely in a fixed location, then I see that having a powerful laptop just isn't worth the money.
If you must work from a coffee shop, just bring your $300 netbook and ssh into your desktop. Why bring a noisy and hot laptop that only lasts for 4 hours when you can have a silent machine that lasts for 14?
Desktops are great for power. Netbooks are great for portability. Laptops are bad at both.