If you are ONLY looking for free stuff/benefits, etc., in my opinion the Moms Panel might not be for you.

However, if you apply and don't get on the panel, you will still become part of the Mickey Moms Club which will likely have some nice benefits next year (no guarantees, but it seems likely they'll do something next year, right??!).
Of course the current 12 of us on the panel are all different, but I think we all mostly signed up so we could help other families plan a better vacation by sharing our knowledge. That was the main "reward" for us. It also has been an amazing experience working more closely with Disney (although we aren't employees, we are independent contractors) on a very new "adventure" for the company. Who would have thought that Disney would let a group of parents share their honest (uncensored) opinions about WDW on their own site. It is fairly revolutionary for Disney, and it has been an honor to be part of the process. We also made some close ties/friendships as a group -- since we all share many things in common!
By the way (as a few on this thread have asked), we are NOT paid to be on the panel. We simply receive a "reward trip" (5-nights, 6-days for family of four) as a thank you for our help on the Moms Panel.
We have three kids, so we did have to pay for the incremental costs for the fifth person. Luckily I had a free ticket from being bumped on a flight earlier this year, so I'm using that. We were also fortunate to find availability at the Grand Floridian, so there is no extra cost for the fifth person (the rooms accomodate five). So the main incremental cost for us will be food and tickets. Not really a big deal, especially since it's only for one extra person.
By the way, if you are interested, there is an even more active thread about the Moms Panel over
HERE.
Also, if you want more details about the contest process last year, I wrote a detailed (perhaps, at times, a bit too detailed

) article about the experience (including my answers to last year's questions)
HERE.
And lastly, but most importantly, BEST WISHES for all of you who are applying for the 2009 Moms Panel. I'm sure all of you deserve to be on it, now let's just hope some Magic comes your way.