We just got off our Cat 3 cruise and the conceige staff was WONDERFUL! I missed the first meeting, because I didn't think I needed it due to having booked my ressies online. Well they called and offered to make ressies for Tea with Wendy and Wine tasting, and anything else I couldn't do online. For the kids birthdays being celebrated onboard they placed a sign on our door and left a certificate and pin as well as pillow cases signed by the characters. There was a food item each night:
1 - fruit bowl
2 - cheese plate
3 - sweets (chocolate strawberries a cupcake and small cakes)
4 - cheese plate
5 - sweets (same as above)
6 - fruit bowl
7 - sorry I can't remember this one.
They also delivered each night the weather for the next day, they delivered all our excursion tickets, final bill, they even brought us and offered to help fill out our customs form. They dropped off the gratuities paper and talked me through the form on the phone (I couldn't remember anyone's name

) at which point I left the completed form in the fish on our door and they dropped off our tip receipts. I never had to go to Guest Services and stand in line at all - they took care of everything.
We not only had priority boarding (we never stood in line for check-in as they had a special check-in window and we were boarded first) but they also told us that for tendering in Cabo San Lucas we had priority boarding and did not have to wait in line for a tender ticket - we just needed to call them and they would take us right on. We didn't need to use this because we had shore excursions, but it would have been nice if needed.
They were so wonderful to DS9 and DD2. Everyday they delivered something for the kids. Coloring Books, Plush for DD2 and Arcade Card for DS9 etc.
They also had a private Cabo San Lucas sail away party for conceige guests with hot appetizers and drinks (rum punch for adults and fruit punch for kids). Although I had a fruit punch -- it was SO yummy!
On our last night they also brought by a lithograph of Snow White and her Prince on the
Disney Cruise - it's a 16 x 20 and really lovely.
This being our first cruise, I don't know if they are always like this but they were truly wonderful! We loved them, and have rebooked a Cat 3 again!
I hope this information is helpful! Personally I felt the conceige service was well worth it. Having said that, I read a thread where someone felt the conceige hadn't done anything for them - including a birthday onboard. My husband and I also celebrated birthdays onboard (all our birthdays are bunched together), anyway, they didn't do anything for my husband - my guess is because it was on the first night and they didn't have any time. For mine they put the sign on the door and I had a certificate and pin just like the kids did. So if you want them to be able to do something, make sure you give them enough time and talk to them. I was suprised by everything they were willing to do, things I had no idea before hand of.