I've been running a WLD campaign using Fantasy Grounds for 2 years now and I love it. Since you'll be playing with friends (as I am) use voice software. It speeds things up and you get to chat with your friends. (We use Skype btw and find it works better for us then Team Speak).
Pros:
I get to play every week. This was impossible before using VT software (3 kids...).
If you run a published module and can get electronic versions of the maps you can drop them right in FG and use them instead of making your own.
The amount of prep time is what you make it. I was entering in all the text for the rooms ect but after the group was hitting 25% of the rooms I was typing up I stopped doing that. Now I just read the text to them over Skype. The only prep work I do is to make tokens for the game and to read up on what bad guys they are going to hit that session (my best guess anyway as the party has a habit of moving in directions I don't expect them too. Hate the players!

).
The players can move their tokens around in real time. Since we're doing one large dungeon I drop the map in and we do all the movement and fighting right on the map using FG's fog fo war feature. to unmask as they move. When a trap goes off there is no question about who is in range.
No travel time! Being able to wrap up a game, take off the head phones and be at home is a HUGE advantage. I can never go to sleep right away after a game but at least I'm at home already.
Cons:
There is an extra cost involved as each person has to buy the software. This was not a big deal for us, but it is for some.
As others have said the game runs a bit slower. Though, I'm not sure by what %. If you fator in the time the party does NOT spend mapping, it might be close to equal. You'll have to see for yourself.
As someone else says above, it is easier for a person to be interupted while they are at home. Phone, kids, rabid pet or a player just watching TV while they play all effect this (yes, I have a player that does watch tv while he 'plays').
Occasional software issues can slow down the game on some nights. This doesn't happen often to us but it does happen. Sometimes someone seems to have connection issues and they'll drop off Skype and FG from time to time (note: this is an advantage to using both voice and FG... if someone loses one you can still talk via the other. If they lose both you know they are having serious issues).
Thats what I can think of off the top of my head. 2 years down and probably 2 more to go to finish up WLD. Then I'll pick up something else and start over again.
rv