Slightly related to the "What spell inflates Aunt Marge?" question.
Can spells be combined to create the effect of casting two spells (but without the time lag involved in pronouncing a long name and doing the "swish and flick" gesture twice)?
Would this be creating a new spell?
Does anyone remember anything in the books that could possibly be ascribed to a character performing two spells together? (Not two characters aiming different spells at the same target at the same time.)
[Slightly off on a tangent too, but would it be possible for a wizard to use two wands at the same time?]