Many Mennonites do use electricity and the internet and such. Mennonites cover the whole range from Amish to indistinguishable from any other normal red-blooded American, so it's best not to make any assumptions (although if they're online, it often but not always implies at least a little more liberal policies than some might lean toward.)

Of course, speaking specifically to my own case, I'm more like the lapsed Catholic - I know the creed, I'm vaguely aligned with some of their beliefs and practices, but when it comes right down to it, I've almost nothing in common with the church anymore and the church as a whole shouldn't be judged on my example.