On my Platinum, the only gym that I had a problem with was Volkner, and it was probably because I was a little underleveled. Not to mention that I didn't have a ground move, and two of my Pokemon were weak to Electric. Took me three tries to defeat him, and the third try was only because I had my Empoleon left (his Raichu died of poison after killing my Togekiss. Thank god for Roserade and Toxic Spikes).