I'm waaaaay to early to worry about stuff like that (22, currently about 4.5 months into my first relationship), but...
I really don't know if I'd even have a chance to fake it. Judging from my...er...."alone time" if you want to call it that, I'd probably get there way too fast. Although I don't think I'd fake it. Also, if she had an orgasm on her end, and I'm REALLY not getting there, I'd probably just stop.
I don't think I'd like her to fake it, and if there's something I need to do better (or she just wants to stop), then by all means, she should just say so.