It's not perfect, but I like the much bigger screen on the laptop over what's generally available on single-purpose GPS units. About the only places I've had trouble keeping a good satellite signal are some canyons in West Virginia where only a small sliver of sky is available. I've been doing quite a bit of work in and around NYC in the last couple weeks and have found that even in most high rise urban environments I've got decent connectivity...not perfect, but decent.
I use a bluetooth receiver that connects to a laptop or PDA. I keep the receiver in the trunk of my bike and have a mount on the handlebars for my Pocket PC.