I am a heavy user . . . of the Multnomah County Library.
Every day, as I'm researching my current writing project, I use books I've checked out of the library. And I use online sources like the Oxford English Dictionary or JSTOR (an ultra geeky research database that allows me to find articles in languages I don't even read, which I then try to translate), which I access through the library's website. The Interlibrary Loan service has gotten me books from all over the country when I need them.
And maybe most important of all, I look out my window every day and watch families walking to and from the library. Which is about the best inspiration a writer can have.
So what does a heavy user and long-time lover do to say thanks? Volunteers to spend the next 4-8 years making the library better for everyone in Multnomah County.