Yep, you can! Odd thing is that, even at the lowest settings, it still appeared really... bright to me? It's hard to describe... it's like the monitor itself was always "burning" my eyes. The small text was more of a nuisance than anything.
I'll throw in my two cents:
I just got my 27" iMac and I'm a switcher. The text on the screen did "burn" my eyes at well at first. I had to really turn down my brightness till I got used to it. I haven't changed the text size, although it was very hard to read at first but I've gotten used to it now.
Yeah, as dumb as it sounds it does takes a bit to get used to these high quality screens. My eyes are still adjusting to the huge screen and high resolution, but it's getting a lot better. I mean, I'm coming from a 19" cheap LCD screen that was displaying maybe half the resolution and it wasn't nearly as crisp as this one.
It's kinda like when I switch from my prescription glasses to my contact lenses after a while. My glasses aren't as good and when I put on the contacts, my vision improves so much that it gives my brain something of a headache because its just not as used to it. But after a while, your eyes adjust and it works out fine.