[R-sig-ME] longitudinal with 2 time points

[array chip]

Hi, I am wondering if it is still meaningful to run a mixed model if a 
longitudinal dataset has only 2 time points (baseline and week 4)? Would it be 
more appropriate to simply take the difference between the 2 time points and run 
ANOVA (ANCOVA) on the difference? what about still running mixed model on the 
difference of the 2 time points, but adding baseline measurement as a random 
factor?

Thanks for sharing your thoughts.

John