I wrote to Hilary late in 2003, maybe November or December, and got an autograph back around Feb 25th, 2004.
I like her old autograph better.
Like most celebs, the more they sign the more sloppy / quickly they learn to sign. Kristen Bell is an example of that too - now her autograph is total crap compared to just 2 years ago. I guess if you sign your name a few hundred thousand times you get sick of it and eventually you just don't care anymore.
I sent a second request to Hilary around January of 2005 and I never heard anything back. One per customer back then, I guess.
Nice success ! Good luck to all who try her.