I dont think it is bad etiquette in *all* situations, but it is definitely only for casual gatherings. For formal events (weddings, showers, retirement/going away/specific parties) I personally find it tacky, like the invite doesnt match the event.
That being said, I did send an evite for my tree-trimming party last year. But I also spoke with everyone I personally invited and it was a 'more the merrier' type of party, so, many people came that I didnt even know.
*Last year I also used to have a standing "martini" gathering once a month. Evite managed all the reminders/rsvps, which made it MUCH easier than tracking it myself.
*a co-worker was moving away and sent an e-vite to join him for a last drink in the city (he had already had his office going-away lunch).
*But for my sister's baby shower, I sent handmade invites (the girls that made them are wonderful!)
Although I did have a friend who simply sent an email regarding her holiday party this year. It's on the same day every year, so everyone just plans to attend. I think this was too casual, but hey, I am not about to call her on the carpet over it.
ETA: YES!!! I am finally a full member (they should change that title to "Fully Opinionated Member"