The RPG book mention that it's about belief, and I think that is best explanation for why it won't work in general. That the wizard has to believe that it's going to work without *any* doubt. Now how many of you can tell me exactly how every aspect of a computer works, down the each nanometer transistors works? Especially considering 45nm manufacture has issues with "quantum leakage" (aka, switch is off, but still leaks electricity). Do you know how atoms work? Or subatomics? Let alone, do you know how a comparatively simple device such as a car engine works?
Personally, I've fealt that the "murphy's law field" is a poor answer. It's more that magic is a wizard exerting his will over the world, and the "hexing aura" is his subconsciousness expression of it. Which is why when big magic is happening, more things go BOOOM. The older the wizard, the less familiarity with "technology", the quicker things go wrong.
Which means even a circle will cause issues as it *is* a magical construct.
Personally, from a story standpoint, using the internet, or computers feels wrong... and lazy. What's the point of having a magical community if all you ever do is sit on the computer (yes, I note the irony in the statement)? That's the point of summoning spirits and demons and other creatures of the Nevernever. More flavor for the game. That, and you'd almost *never* need thaumaturgy!
That being said, magic circle, Windows, speech recognition. It works GREAT. I use it at home all the time. Works great. Though, you'd want to pick up that extended warranty, and that's not a "just in case". that's a "for when it happens".