<< What are the expected price decreases, if any, that laptops will undergo in the next few months?
Yes, I would definitely WAIT as long as you can. A co-worker of mine needed a laptop for school, I told her to wait, of course she didn't listen and bought an IBM ThinkPad (Celeron 600/128/20/DVD) for $1,100 back in October. She didn't need the laptop until this month, she could now buy a P3/1GHz with better LCD display, NIC/56k modem, DVD, and Windows XP pre-loaded for the same price.
<< Do laptops suffer depreciation as fast as desktops do? >>
Yes, more so. A desktop you can easily upgrade by buying standard components from newegg.com