I've had both. When I had a job that required me to travel, having the laptop was nice for the hotel room, preparing and doing work on the plane, etc. etc. Now, my current job doesn't require me to have a laptop, and I am not missing it at all. If i need to jump online really quick to check email or check movies times, I can use my wireless PDA that boots up a lot faster.
I personally prefer spending my money on a desktop due to the fact, i can upgrade parts as necessary, and when stuff breaks, I can go to the local computer store, buy the parts and fix whatever broke in the same day.