[CalmLogic]

Yeah, I agree. Congratulations on getting into Brown!

I am interested in NLP, AI and data mining/text mining in general.

All the more reason to go to Brown, as you have seen:
Brown Laboratory for Linguistic Information Processing (BLLIP)

I don't see any such lab at UCSB's website. Furthermore, Brown ranked #17 in AI in USNews in 2006. I would think the latest 2008 rankings would be similar if not better. Neither JHU, USC, or UCSB ranked in AI in 2006 as USNews only ranked the top 20.

UPDATE: However, I would wait for word from JHU since they do seem tempting:

"This will be the nation's premier language technology center, and it's likely to stimulate further expansion both at Johns Hopkins and at the University of Maryland in this important research field," Poehler said.

Headlines@Hopkins: Johns Hopkins University News Releases (June 2007)

As you have seen:
Natural Language Processing Lab home page
The Center for Language and Speech Processing at JHU

You would know better than me if JHU is better than Brown for your interests, but I would wait for JHU's decision, just to be safe, at least. Maybe they will offer you a partial tuition waiver

MSE students may be granted a tuition waiver between 10% and 50%, with 50% being alumni. MSE students are never given a stipend of any form.

JHU Department of Computer Science

or an even bigger surprise:

Applyed as MSE but accepted as PhD with full support

computer science hopkins • thegradcafe.com

I would not, however, turn down UCSB unless you already have documentation for an I-20 to pay the tuition at Brown (assuming you are an international student not eligible for U.S. student loans):

Tuition: $35,584 / year
Brown University - Engineering - Best Graduate Schools - Education - US News and World Report

Tuition: $14,988 / year

University of California--Santa Barbara - Engineering - Best Graduate Schools - Education - US News and World Report