Skaters who definitely stayed past their prime:
Elena Liashenko
Hard to say if she ever really had a "prime," but if she did, it is well behind her.
Elena Sokolova
She is now 3 years past her brief peak in 2003. And in all the years before and since 2003, she has been a mediocre and disappointing skater. Time to move on.
Maria Butyrskaya
When she retired in 2002, it was past time. She definitely peaked in 1999.
Angela Nikodinov
I love Angela, but she probably should have retired after failing to make the 2002 Olympic team.
Michael Weiss
In the last few years, he has obviously been hanging in just for the money IMO.
Tim Goebel
He probably should have retired after the season when his whole body got out of alignment (or whatever that situation was).
Takeshi Honda
His season this year was nothing short of disastrous. Sometimes you just have to know when to stop.
Sasha Cohen
I know this is going to be controversial, but I really think Sasha should retire now and focus on show skating. It has become crystal clear (to me at least) that Sasha simply does not have what it takes to win Olympics or Worlds. This year, she had the best opportunities she'll probably ever have to win both those events, and she still couldn't do it. Meanwhile, all the drama surrounding her and her mental state is IMO becoming distracting and annoying. I think she should cut her losses and focus on what she does best--which is beautiful, artistic skating. I am ready for The Sasha Show to end, at least on the competitive circuit.
Petrova & Tikhonov
There was no improvement in their skating after they won Worlds in 2000. Why continue for six more years?
Zagorska & Siudek
Same as above (except their peak of course was winning bronze at Worlds, not gold).
Scott & Dulebohn
I really don't know why they kept going as long as they did.
Skaters who might *appear* to have stayed too long, but IMO did not:
Michelle Kwan
There are many who argue that she should have retired after 2002. And there is little doubt that Michelle hit her actual athletic peak well before that, probably in the late 90s. However, I still am glad that Michelle carried on from 2003 to 2006. Because the fact is, even if she was no longer at her peak, she was still one of the overall best skaters in the world, an assertion borne out by her competitive record during that period: gold, bronze, and pewter placements at Worlds in 2003-2005 (not to mention three national titles). And many beautiful performances besides. I personally am very glad she stayed in for that time.
Brian Boitano
In terms of results, his 1994 season was definitely disappointing, and he was clearly a bit past his peak athletically at that point. However--I loved his programs that year. His Appalachian Spring long program, to me, was an artistic high point. I still enjoyed his performances, and he acquitted himself respectably at the Olympics, even though he didn't medal. I'm glad he came back that year.
Todd Eldredge
The thing that impresses me about Todd is that he kept his skills strong throughout his whole career, right up to the end. I was glad he competed as long as he did. Todd just happened to have the misfortune to skate concurrently with three men who IMO are among the most brilliant and/or innately talented in the history of the sport: Kulik, Yagudin, and Plushenko. Todd was extremely talented, polished, and well-trained, but didn't quite have that extra level of brilliance that the 3 Russians brought to the table. Nonetheless Todd was a wonderful skater--always solid, reliable, and enjoyable to watch. I'm glad he stayed in as long as he did. At no point did he embarrass himself or the U.S. team. (This in my mind is always an indication of having stayed in too long. For example, Sokolova's performance at the Olympics this year is what I would consider simply embarassing.)
Lu Chen
Some might argue that she should have retired after 1996. And clearly, 1995 and 1996 were her best years. However, if she had retired then, we would have been deprived of her beautiful performances in Nagano. Her Olympic bronze medal in 1998 was inspiring.