A lot of good points being made here...take it from a designer of more than 15 years--I have a Powermac G5 tower, a Powerbook G4 (5 years old, still in use), a Macbook white, and a Powerbook 12 inch G4 (5 years old, still in use). I use ALL of these systems on a regular basis for different design realms. I design for all mediums--broadcast, print, web, mobile--and obviously the bigger the job, the more horsepower you need. I even run After Effects on the PBG4 15 inch, and have been for years! But for web, all of these systems work just fine.
In fact, I purchased the Macbook specifically for a web design station due to the fact that both my wife and I share this side of the business, and with our busy lifestyles we never know where we'll be. We find no issues with the 13 inch screen. You just have to get used to it, but we don't feel like we're giving much up. It's just a matter of adapting and accepting it for what it is, which is a monster machine in a little box, for $1000 price point. I've even installed Final Cut PRO (not Express) on the white Macbook and it works perfectly. Naturally there are limitations, so to the video gurus out there, please don't jump on me. I still use the desktop as the primary editing station, and I'm just trying to prove a point for this thread.
If you're typically at a desk, buy a refurb Apple Cinema Display for $499 to increase your workspace. Then take the laptop mobile when you need to be on the go. So for around $1500 you can have the best of both worlds--and the cherry on top is that you'll be a Mac user and can reflect nostalgically on the days you were not.
By the way, I'm about to purchase a Macbook Pro as my primary mobile station to replace the PBG4 15 inch, and I will push it as hard as my desktop G5. If you're cautious about spending $2k on a laptop, spend $1k, and get yourself most of the way there. You will not be disappointed with the Macbook.
