@Cori: These are their "official titles" - Soshified has the most useful profiles on all the girls
Leader: Taeyeon
Lead Vocalist: Taeyeon, Jessica, SeoHyun
Supporting Vocalist: Sunny, Tiffany, HyoYeon, Yuri, Sooyoung, YoonA
Lead Dancer: HyoYeon, Yuri
While Yuri is often the focus over HyoYeon, Hyo is the group's "dancing queen", she's only just been getting the love she deserves with this album cycle...against Yuri, who is one of the "faces" of SNSD, Yuri wins in terms of media focus!
So I guess you could say that TaeYeon, Jessica, SeoHyun, HyoYeon and Yuri are the "main players" in the group, with the others relegated to supporting roles. However, in the world of KPOP, they need members who are good on variety shows, those with model's looks for magazine covers and endorsements and those with huge personalities to attract attention. None of the members are "useless" within SNSD but not all their roles are pivotal for their music!
I only have a Gen 1 iPod - that game won't work for me, will it?? ;_; They need android stuff too!