@Montana, I've seriously been considering doing this myself. I only have about 12-15 people coming.
I had planed to have everyone share their information on a form on my wedding website. But now I think about it, I'm sure people will forget to supply me with the important information and it will cause stress. I'm sure I will have to hound people about booking flights and rooms. Since you are paying for so many you wont have to do this, but if your paying for their flights, you will need their personal information to book the flight.
I finally found a Travel Agent/Consultant that isn't trying to push me into something I don't want and I think I can work with. I'm a AAA (the road side assistant) member and they do this for free with membership so I'm going later today to talk with someone about what they can offer me. Every travel agent keeps making a point of, if you book online then you have no one to call when something goes wrong, with us, you have a live person and a phone number.
Something frequently I hear on this site and every other place that destination brides talk, is that they have trouble getting in touch with their on site wedding coordinator. My resort doesn't really respond to questions until about 2 months out. I've herd about timely communication being a big issue from people at many different resorts. They all say once they are there its wonderful and the people are great. This is another reason I'm considering a travel agent. They can get answers from the resort's faster.
I was originally thinking of just contacting the resort and asking for a group rate, but then again I can't be sure how many people will actually come. I'm a year and a half away, and most people are saying they are coming, but I'm sure once it comes down to having to pay things may change.
It couldn't hurt to ask your resort.
Also, watch pricing for your resort. I've been watching pricing for my resort for about 6 months and saw that booking through the resort's website is cheaper than the online travel websites (Orbits, Travelosity and so on) and the resort also offer specials. Mine offered something like if you book so much in advance you get 15% to 35% off.