I've just come back from a Club 18-30 and here is my opinion of it.
When you first arrive at the hotel (which was 7.30am for us), you get checked in then the reps inform you that there is a welcome meeting for you to attend later in the morning, (about 11am or 12pm).
At this meeting they tell you what they've got lined up for you on your weeks holiday (we were there for two weeks so they were going to tell us later in the first week what was lined up for us in the 2nd week).
So, they run you through what activities you can do and what they involve. Then they offer to sell you all these activities for something around 220 Euros (£154 approx.) Or (as we did) you can buy the activities individually. We only went on the activity called 'Boat Selecta' which basically was a bit of a booze cruise with two stop points for swimming and sun-bathing. We ended up only stopping the once because the sea was a bit choppy.
The only trouble with buying these activities was that you had to buy them on your first day there so that they could organise the tickets.
Going from what people told me there, (who had bought all the activities in one go for 220 Euros), quite a few of them have said that they weren't all that good, or worth the money. The foam party was a waste of time. Apparently, these 2 girls left the club at about 2am, having had about enough to drink (because of the free bar I guess) and the foam hadnt been dispensed yet.
Anyhow, the reps were great and had great senses of humour.