Wow, okay...
You guys must not DM/GM. The DM/GM cheats die rolls and abilities all the freaking time (well, more in Roleplay driven games than in tactical) for the sake of plot progression or just saving the party from an unhappy mishap (occasionally, most the time I just let it fly where it may and watch the fun of them recovering). As a GM, you're taking on the role of an entertainer, if you are so egocentric as to cheat rolls to that your monsters crit, then you're forgetting the main reason behind running: To let everyone have fun. If your players are dying because you choose to buff your own rolls, then they probably aren't going to have fun, and they are more than likely not going to stick around.
Let me also explain something else: The DM/GM technically can't cheat. If he says a bolt of energy flies from a god's rear-end and strikes your character dead, then he can do it....without a roll at all.
My suggestion is a tool for us GMs who use 'cheated' rolls to help the party or the plot, not for some half-wit kid in a Metallica T-shirt looking to prove how awesome he is by fudging rolls so -his- cool character's will be the shining stars. Will you get that? Maybe. I'm not arguing its something that could be abused, but at that point, you just stand up and walk away because that's not a good mindset for the person who is supposed to be taking you through a fun and exciting adventure where your characters are the heroes.
Cheating the rolls...heck, cheating the system and making the rules work for the situation is why you have a GM in the first place...someone to mediate and make calls for the progression and enjoyment of a shared story or adventure. The GM should never be in the mindset that he is against the party, and if he is, he needs a few lessons. Sure, some of the character he takes control of -are- against the party, but in the end, its about the PC's being the heroes.
Also: "i say go somewhere else?"
Who are you?