Originally Posted by Marvin
Did you get it with or without the optional go faster stripes stickers? Apply stickers to improve the perception of speed. The quad-core MBP is over twice as fast as the old one in both CPU and GPU but you'll only see that performance difference if you do things that stress either of them e.g if you encode movies with Handbrake, if you play games or use certain resource intensive apps like Adobe apps. For average use, there's going to be very little discernible difference, which is why the mainstream computers (the Air) are on ULV processors.
I have a sticker on my own notebook. I considered looking for a circular yellow one. I would place over the Apple logo, then use an x acto knife to trim out the inner part. It would look like the Apple equivalent of the bat signal, which would be awesome, even if the bat portion was normally the shaded part. I find if you really utilize them the quad core machines are significantly faster. The OP never really mentions what was slow about his old one.
I would say it varies. I don't like to give out generic performance advice, because it does vary. If most of your time is spent in one or two applications and everything is loaded, the difference will be nearly unnoticeable assuming you are completely unconstrained in terms of ram. 4GB is really tight with Lion and ML.
There's far less chance of beachballs with an SSD and even just general delays in opening apps and files because of the IOPs especially random read/write performance. 8GB+ RAM is a good idea too but check if your page outs are high in Activity Monitor. Ideally page outs should stay in the low MBs or even 0 for long periods of time if you have enough RAM. If it's GBs after less than a few days, a RAM upgrade is worthwhile.
In case he already owns a copy of disk warrior, that helps too. Part of it was a software problem, but back when I was limited to 8, there were times where I had 40GB or more of pageouts over a few days. SSDs make that less noticeable, but ram is still ideal for what it costs. It's important to actually know what was lagging to provide a good answer for the OP. Otherwise he will end up spending more than necessary.