Watch out for the tank leaking from around the hinge at the rear, weeping fork seals and seized rear brake callipers. Also if you drop if the forks will put a dint into the tank!
When riding it the lack of steering lock might catch you out.
Someone once said that the quickest way to do a U turn on a Monster was to park up at the side of the road, wait for another Monster to come along from the opposite direction then swap bikes!!
Popular mods would be going down one tooth on the front sprocket and if you are feeling flush a twin disk conversion on the front. Also many owners cut down the tea tray at the rear as its rather huge as standard. A longer front mudguard stops spray soaking the front cylinder and making it cut out.