If you even begin to attend the thursday night meeting you will hear a LOT about donating, from 'account reports' (a monthly notice that the Kingdom Hall is behind on all it's bills and not enough $$ was given to cover expenses), to special 'announcements' to remind the people to give. No no donation plate is passed around, but the donation boxes are hard to miss at the kingdom hall. Pretty much every thrusday night we had some announcement about $$. Studies are not usually invited to those meetings right off, they start you at the small bookstudy or Sunday 'public talks'.
Even though they 'give away' the books, the local cong MUST PAY the WTBTS for each month's lituature shipments, usually in a 'donation to the worldwide work' that comes out of the local cong funds. If they fail to pay, they WILL NOT have more books shipped to them. This is VERY hush hush, but all the accounts servants know about it. So in turn the local cong pressures the local JW's to contribute to cover those costs. Sometimes JWs will suggest to people at the door that they may contribute if they'd like to, but most JWs I know are not very comfortable asking for that and just pay for the books themselves. The WTBTS leaves little coded hints in various places as to how much to pay for different things usuing words like "similar CD-ROMS cost as much as $50-300" or "you could mention that similar books sell for $5", etc. This is a way to communicate 'how much' the JWs should contribute for each item without outright setting prices (which would get them into tax trouble, which is the whole reason they stopped charging for books in the first place).