Being a Disney CM, let me tell you these cards are great. Most CMs feel very under appreciated from Guests, and its always been human nature to point out negatives, but never to point out positives. I guess so many people expect us to be happy all the time that when we go above and beyond what even we are expected to do, they feel its normal.
Even better, is to write a letter for the CM to Disneyworld. Be as detailed as possible. Guest letters are EXTREMELY rare and are very VERY importatant to us. The entire monorails department may receive 5 letters in an entire year that explicitly address a cast member. Maybe 10 a year in total that address monorails. Be specific with the Cast Member Details (Name, Hometown from nametag and a brief physical description). In Monorails we don't generally know where someone worked the day before, so just saying John at the Magic Kingdom doesn't get the credit to the CM. Saying John, from Milwaukee, an older gentleman with glasses will.
If you aren't the letter writing type, but a cast member has gone above and beyond for you, just ask to see their manager and compliment them to their manager. It may take about 10-15 minutes for a manager to arrive (Look at the area our department covers) but it is truly one of the highest compliments you can give a CM. You are basically telling their manager, that the actions of this CM where so outstanding that you felt it necessary to take time out of your vacation to have their actions be known.
Hope this helps you know how our internal feedback works. We're here for you, and while sometimes we may forget it, we all know that if it wasn't for our guests, we wouldn't be here.