The i7 brings a new and more powerful core to the table
The C2Q's are not hyperthreaded and the i7 is.
C2Q's do not automatically overclock themselves and the i7 does (turboboost)
C2Q's have an external memory , the i7's are built in C2Q's have 4mb cache versus 8mb for the i7 (typically)
The Q8 series of the C2Q's do not support SSE4 instruction set (Q9 series does) and i7 Does.