In saying "powerful enough", I assume Dave is also thinking that the laptop needs to have provisions for handling a 2nd hard drive, since that can be one decided advantage a desktop system offeres. Generally too, the laptop will not have hard drives that perform as well as a desktop system. As for the LCD color issues, at least they can be worked around by connecting an external monitor. But, if I’m going to hook up a monitor to a laptop, then I may well decide to forego the portability of a laptop for the lower cost and greater flexibility of a desktop system.
Another "powerful enough" thought…and perhaps more relevant…is "powerful enough for your needs?". That is, if all you are doing is image editing for the web, working mostly with smallish image files, then even the need for multiple hard drives might be a lesser concern. So, consider what you’d envision your usage of Photoshop on a laptop for, both in terms of immediate plans and those you might anticipate down the road.
Regards,
Daryl