There are loads of different ones. The Dublin Chamber is by far the biggest.
I was a member of another one when I started out. Like with a lot of things in life, people expect immediate results. You'd get someone new making a presentation about what they did, never come back and cite a lack of response to their presentation as the reason. No one knows them. A Chamber is about getting to know people and maybe creating opportunities over the long term. I got bits of business from the Chamber. But I have made lots of contacts that I use to refer business to for conveyancy and tax advice. I work in an office share and met the guy who runs it from the Chamber.
If you want to get new business, and quickly, join a business network. But remember, everyone is looking for referrals, so you better give as well as take. If you want something that's a bit more slow paced, a Chamber can have its benefits and you will find people you connect with and can learn from. You make get business after a while.
When someone is giving a referral, they aren't doing you a favour, they are doing their friend a favour. They are also putting their reputation on the line by saying you are the best person to solve their friend's problem. They don't want to look bad if you mess it up so they will want to trust you and know you for more that 20 minutes before they are going to refer business to you.