As I said, best to show her face now and get it over and done with. People will cry, rants will be made, vengeance sworn, but it will eventually die down as people realise that it is done now before it gets boring. If they don't show her face, we will have threads like these for years to come, and every Mass Effect game produced will have "Will we see what Quarians look like in this one?" threads and debates. 'Artists' will continue to draw up fanpics of Night-Elf Tali doing horrific things with engineering tools. Debates on their physiology and why one poster's theory is obviously correct over anothr's because they make Tali look like a Night-Elf... Do you really want that? Do you?? For the love of all that is squishy, don't doom us to that fate!! 
I just wanted to quote this for all the Tali haters, because it's very true.
If her face is revealed, we'll have at most a few months of some people with stupid expectations being upset, and then you will never hear about it again, and people can move on with other aspects of Mass Effect.
Not showing her face will drive those people into overdrive and they won't stop until another game which reveals the Quarians is released, and that could be years and years down the pipeline. Imagine Talimancers effecting every ME game for the next 5 years. Do you want that?
It makes logical sense to reveal her face. They've teased for two games, and now they'll show it, and that will be the end of it. We don't want to drag this out in a decade long saga. It's not healthy for the franchise or the playerbase.
And for all you "keep it a mystery" people. Honestly, most of your "imaginations" of Tali fit somewhere along the line of generic beauty. There are some of you that honestly want Tali to look like Predators, but those are generally the outliers. If Tali turns out to be a generic pretty girl, with a few cute alien features like I said before, most people will be happy.
I can't state this enough. "Keeping it a mystery" is a horrible, horrible idea, not just for ME3, but for future ME games.