Some general impressions:
It's a lot lighter than a traditional hard drive, and also runs much cooler. Though I've never noticed heat coming from my old HDD while in my Unibody Macbook, which I can't understand because I have no idea how Apple is cooling it. I'm guessing/pretty sure my battery life has increased with it. I'm sure the 34nm process helped with all of this.
As far as actual performance gains go, once the computer has booted to the desktop, it's immediately completely usable. Resumption from sleep is likewise a little faster as well. This really brings to attention how long the computer takes to connect to the router, as the computer is ready and rearing to go while the airport is still deciding what to do. Snow Leopard will really help with this.
Otherwise, I haven't done anything intensive yet to test the performance, but altogether, it is as if a lag that I didn't even know was there has been removed from the computer, and it's like I can't believe we've been living with this laggy performance in our computers for all these years. Is it lightening fast OMG amazing!! ? No, I wouldn't really say that it reaches the hype and fabled performance gains that people tout when they're talking about SSDs. A lot better, yes, but like most hardware upgrades to an existing system, in most cases, it's like, "Is this it?" Though I would have to say that out of any hardware upgrade that I've ever done, the SSD has made the biggest noticeable improvement.
But like I said, all I've done is booted my Macbook and launched a bunch of Apps. I haven't really done anything too intensive yet.