Having switched back and forth between premium and non-premium a few times, I can tell you there really IS a difference.
I can also tell you there are still times when the web site is extremely slow despite having a premium membership. 99 times out of 100, it's because Admin is tinkering under the hood, so to speak.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).