Kayles got a good idea there Paul.
The thing with using a computer in general for production is its a compromise when it comes to actually choosing the machine.
You either go big and immobile - a MAC PRO or similar PC tower. Never moves, full of juice and everything. Pretty much becomes an installation in your room.
or you go smaller and portable - a laptop like yours.
but then you have to deal with sounds.
If you go all mic recording (say you are a singer songwriter always recording yourself and your guitar only) then its minimal. An interface and a mic or 2 and you are good.
If you use a lot of virtual stuff, then you have to figure out where to store and stream the sounds from. Then you have to do a little research into how portable and how robust those streaming sources are going to be.
two things that you can count on to begin with:
filling up a drive of any kind to capacity makes it run slower.
A mechanical hard drive slows radically (exponentially actually) once you fill it more than 50% full. This isn't so much of a problem these days cause mech HD are very inexpensive per GB. You can get a 1 TB drive for about $60. As Kayle says, 7200 RPM with a decent size cache like 32 MB or bigger, and an interface speed of 6gb/s (SATA III) is the type to go for. Long term reliability for mech HD is poor - you can be sure it will fail sooner or later especially with heavy use. Most mech HDs come with 2 or 3 yr warranties, although some like the Western Digital Caviar Black 6 gb/s drives are 5 yrs if I am not mistaken. The extra money is worth it cause replacing drives is a major PITA - its happened to me on a number of occasions over the last few years.
a solid state drive (or which USB keychain flash drives are very closely related from what I know) operates best when you have 20% or more of the drive open. SSD's have better long term read / write rates than standard keychain drives usually. Again SSDs come in 3 gb/s (SATA II) and 6 gb/s (SATA III) and the 6gb/s ones are the ones to go for. You also get a choice to spend more money up front and get a "pro" model which usually has a 5 yr warranty vs. a 2 or 3 yr warranty for the standard models.
So putting 128 GB of samples on a 128 GB drive probably is taking a performance hit right there. I usually try to figure out my near-future space need is and double it.
There are other options for portable streaming drives out there from OWC among other places:
http://eshop.macsales.com/shop/firewire/on-the-go or
http://eshop.macsales.com/shop/external ... -Envoy-Pro again trading dollars for performance.
The other issue is how to connect all this stuff to the machine - with a laptop it makes it more and more of a fixed installation but if you get a "dock" and connect a variety of peripherals up to it, it makes things a little more organized. Something like this:
http://eshop.macsales.com/item/Elgato/10024010R/ - and there are always newer and different models appearing.
good luck!