For all intents and purposes, the Latitude is basically just a sturdier Inspiron. The other real difference the Latitude has over the Inspiron is the inclusion of a smartcard reader under the PC card slot. I believe the new Inspiron as include TPM so that is one other difference out the door. Policywise the Latitude is only sold through the business section of dell so they get warranty and support options not available through the home section.
Another secret Dell does not really want to let on about is that the Precisions are really just Latitides with a different BIOS. Dell fux0red up and sent me a mobo without the proper BIOS . After swapping out the board, the laptop booted as a Dell D610. The support guy quietly sent me the proper BIOS and a few things changed. The biggest one being the ATI Radeon X300 became a ATI Fire V-series.
I prefer the Latitudes because they are a bit sturdier and Dell's Gold Support (if you choose to get it) is a hell of a lot less annoying than Dell Home Support. When you call in a problem, Gold support does not play you for an idiot and they take your word that something is broken.