Been there, done that, got the t-shirt ... this is very common. It doesn't make it more pleasant, or less annoying. And it is not just endemic to skating: my littlest is a very talented musician, and we've discovered that nastiness and resentment come into play at recitals too (fortunately, recitals are less often than daily skating sessions). Fortunately, she's deaf in one ear, so, she doesn't hear a lot of it !
Any time you have competitive parents you will have this type of behaviour; my son gets it on the baseball diamond, we got it when he was moved into an advanced academic program that their kids didn't get into ... etc etc etc. That's when your kid learns a hard lesson: that true friends will be happy for them, but, false friends won't be, and also that modesty and perspective are important character traits to demonstrate.
Now, we also reminded our kids of how upsetting this behaviour was when, in later years, other kids began to achieve things faster than they did, and told them that we expected them to demonstrate good sportsmanship and positive social behaviours.
Take the high road, learn to smile mysteriously, wear an iPod (even it it's not turned on) - and always respond with as little gushing about your kid as possible: "Yes, thanks, things are going well right now." - is a good response - particularly followed up with "and your daughter's [insert something you can compliment here, whether it be expression, edges, turns, dances, choreography, ANYTHING] is looking great - glad to see it!" - and then leave it at that.
And, don't get caught up in the "uber mom" group - where the parents of the kids who are doing really well all hang out together, sit in the "best seats" and criticize everyone else's kids and loudly praise each other's kids to draw attention to every accomplishment ... sigh.
Beware of skating mom "friends" - step back and think, hmmm ... if I met this person somewhere else, and we weren't stuck together in an arena for hours, would we like each other? Is this a person I really am interested in? If not, and it's just proximity and convenience ... then, well, maybe discretion is the better part of perhaps getting caught up with somebody who really isn't your cup of tea.