Following on my comment above, while users may often want to see filtering conditions ANDed together, there are often sub-selections WITHIN condition categories that further define those categories.
Think of Amazon's faceted search; items you search on have multiple categories, and if an element of a category is selected, that CATEGORY becomes an AND, a required element in the search.
But in some categories you can select multiple sub-options that are ORed together. For example, in the hard drive example below I could select Amazon Prime, and I would be shown only hard drives that qualify for Amazon Prime, in addition to any other criteria.
I could also select three different choices in the Brand category, and it would show me ONLY drives from the brands I'd selected; the brand category becomes ANDed with Prime and my search term of "Hard Drive." But within that requirement of a brand, it would include only drives from brand 1 OR brand 2 OR brand 3.
I could easily see a case for searching for "People who are in Boston AND have a masters degree AND have more than 5 years of experience, who are also EITHER a designer OR a researcher and who are EITHER looking for full time OR contract work."
A more robust faceted search-type system could work well in a case like that.