I only need current projects on my laptop and not my entire image archive, but this is how I do it:
If the project started on my desktop and needs to go to my laptop, I export the relevant folder or collection to it's own catalog. I check the box to include smart previews and uncheck the boxes to include originals and to build standard previews. My export location is to a Dropbox folder.
On my laptop, I just go to the Dropbox folder and double click on the exported catalog. This opens it in Lightroom with the smart previews. Smart previews are 2560px on the long size which is good enough for most editing and for small exports. I make edits as needed which are automatically saved back to Dropbox since that's where the catalog is. When I'm ready to get those edits back on my desktop, I choose "import from catalog" in the menu and select the option for metadata only. I may do this back and forth several times for the duration of the project, then I delete the catalog from Dropbox when I am done with it. All pictures and edits still live on the desktop.
If the project started on my laptop and needs to go to my desktop, I will do a fresh import on the desktop from my CF cards or an external drive, then export the catalog from my laptop to Dropbox (metadata only) and import from Dropbox to my desktop (metadata only) to get the edits on there. It's a fairly simple process that only takes about 2 minutes in each direction.
I could just as easily use that same process to keep my full library on both computers (smart previews only or full images), but I have no need for that.