The Big Disclaimer

This has to come first: the Monster emissions system is mandated by the state of California. If you live in CA and choose to modify or remove it you could be facing big legal troubles. Here's what the CA Air Resources Board (ARB) has to say:
"Along with other motor vehicles, the ARB has identified on-road motorcycles as a potential source of air pollution which can be reduced cost effectively. We are currently meeting with on-road motorcycle manufacturers and other interested parties to determine appropriate emission control requirements for these vehicles that reflect the latest technology advancements."

Up to you, but you've been warned. Don't do it.

What can I expect from doing this modification?

Well, don't expect an increase in power. In fact the main effect of the emissions system is to recirculate gasoline vapors into a charcoal cannister. The irony is that there is a parallel system that dumps excess gasoline (from overfills) directly to the ground. Plus, it isn't really clear how long the charcoal cannister remains effective. The only reason to do this modification is if you're not interested in looking at the kludgy thing on the right side (or rear) of the bike anymore and want to save a pound or so. The good news is that it is super easy to do.

So how do I do it?

There seem to be a couple of different systems. On older bikes it appears as a black cylinder that runs horizontally before the rear wheel. On newer bikes it looks like a small battery and sits on the right side under an aluminum protector. Fortunatly there are excellent articles already written on the how-to, so there is no need to re-invent the wheel:

DucatiSuite.com has a great article on removing the old-style system.

Duc.org has instructions on ditching the new system.

An alternate method to using 3/8" vacuum caps for sealing the throttle bodies is to take off the barb fitting and use an M5 (metric) bolt and some loctite to plug the hole. A kit is also available at TPO parts.

Now, if you have the new-style system you'll have to decide what to do with that goofy right side cover with the big bulge. Options are to take both right and left off and have a real "nekkid" bike, or get a pair of carbon fiber or euro models without the bulge.