I either reply "I work for a law firm", when I'm in mixed company and don't really want to talk about work. But this seems to make people think I'm a lawyer, and I have to explain I'm definitely not a lawyer, but a librarian, and that all sorts of people other than lawyers work in a law firm. So, actually, that one kind of backfires an the -lets-not-talk-about-work front, and I'm trying to not say that any more!
Or I say "I'm a librarian for a law firm", which is what I use when I'm feeling a bit more chatty, and happy enough to explain what I do. And since I end up having to explain my job anyway, I'm using this one more frequently.
No matter what I reply though, both lead to the same response.
The puzzled look.
Then there's a couple of options:
"Oh, I didn't know lawyers needed librarians"
"Oh, do you look after a lot of books then?"
"So, what do you DO all day?"
Is it really so hard to imagine? Is it so difficult to understand that law firms are actually pretty modern places? That the staff, both solicitors and support, do a huge volume of their work on computers? That they have access via those computers to internal current awareness services, subscription databases covering legislation, cases and journal articles, various core legal materials from the Government, sector-specific blogs, CD-ROMS and internal knowledge banks? Of course there are also traditional hard copy resources too: textbooks, journals, case reports, and loose-leaf publications too.
And someone has to be involved in managing all those resources, and doing the frequent research in lots of areas that is needed in an active law firm.
So no, I don't look at books all day long: I look at a computer. And I like it that way.