Her music is VERY under-rated. "A Little More Personal" was an amazing album and she can actually sing. Acting wise, she is just a little under-rated but not much.
I think her singing is highly underrated. People are quick to call her a Hilary Duff/Ashlee Simpson thing, but for some reason when I hear her sing I hear some potential.
Because of all the tabloids and such, the name "Lindsay Lohan" has become overrated, but as far as her talent, which as been displayed from "Parent Trap," "Freaky Friday," and ultimately "Mean Girls," she is underrated. Musically, her "Speak" album was much better than "A Little More Personal."