If you plane shift to another plane, do you now count as an extraplanar creature for the purposes of spells like banishment?
From the SRD:
This subtype is applied to any creature when it is on a plane other than its native plane. A creature that travels the planes can gain or lose this subtype as it goes from plane to plane. Monster entries assume that encounters with creatures take place on the Material Plane, and every creature whose native plane is not the Material Plane has the extraplanar subtype (but would not have it when on its home plane). Every extraplanar creature in this book has a home plane mentioned in its description. Creatures not labeled as extraplanar are natives of the Material Plane, and they gain the extraplanar subtype if they leave the Material Plane. No creature has the extraplanar subtype when it is on a transitive plane, such as the Astral Plane, the Ethereal Plane, or the Plane of Shadow.
So, assuming your PC is native to the material plane, if you go to, say, the plane of Air, you can be banished back to the material plane.
However, if you are on a transitive plane (Astral, Ethereal, Shadow), no creature counts as extraplanar, so no one can be banished.