playstation hard drive upgrade?

I'm thinking I wanna try to do this thing. A few questions for ya'll because I have not idea what I'm doing:
 
What size hard drive do I need? (as in actual size, like in inches)
 
Anyone have suggestions for hard drives to use that maybe happen to be cheap?
 
Is this even a good idea? How many of ya'll have upgraded hard drives before?

2.5"  (laptop size)
 
Try newegg or something, they're very good about being cheap. _edit_ Maybe start here.
 
I went from 80 to 500 for $90 and that was two years ago, I have about 130 gigs left. So yeah, definitely a good idea if you are gonna use it as a primary device for everything.

it's like 2.5", i don't think it matters on what drive brand you use. i'm thinking about either buying an external hard drive or an actual hard drive.

I upgraded to 500G.  Haven't had any problems.   Here is a guide: 
http://www.gamespot.com/features/6176090/index.html
 
 With the PS3 it is really necessary to upgrade to a big drive.  The games use up quite a bit of hard drive whether you like it or not.  
 
It is very easy. Go for it.