1) Is it easy to replace my hard drive with a solid state drive?
2) Is the performance improvement noticeable?
It's easy, but replacing your Superdrive with an optibay and hard drive is harder.
The performance is awesome. Apps launch in no time, booting is really fast. It's so much more responsive.
Intel SSD's would be more reliable. However, I read something that OCZ now has the same supplier for controllers.
I've got some bad experience though. My cable between SSD and motherboard went bad twice. It's a 30 cable. And then there's the man hours you've got to pay to fix it.