I've been to several both here in the UK and in the USA. As a member of the Romantic Novelists' Association (UK) I regularly attend its conference. There is a choice of three workshops/talks for each session, usually three in the morning and two in the afternoon, with the opportunity to speak to agents and publishers. The conference is held in a different place each year, usually taking advantage of university student accommodation and conference facilities. I've also attended the Pen Writers conference, held in Pittsburgh. Again, the conference is a mixture of workshops/talks. Like the RNA Conference, there is an opportunity to pitch to an agent/publisher, as well as the chance to socialise with other writers. They can be costly, and not all conference release details of the workshops before you make payment, so it's worth doing some research by looking at a list of the previous year's workshops before making a final decision whether to attend.