I've worked w/ a 13" for 2 years and while it wasn't the most comfortable thing, it was manageable. I had taken  couple of screenshots...
 
Arrangement, showing 50 tracks. Not the maximum, but pretty much the limit of useable for the basics. 

 
Through the use of clever tricks like the disclosure triangle, Apple manage to grant users access to a maximum of information with a minimum of clicking/scrolling. In this case, you can see the clip properties displayed at the top of the inspector - clicking that triangle will collapse/expand those info and parameters, making it easy to manage screen real estate efficiently.
 
And a mixer shot, still on my MBP 13".

 
As you can see that's a lot of info available at a glance - 6 inserts, 8 sends, EQ graphs and there's still room for more. Again, clever tricks like color coding allows you to know which sends are pre and which are post at a glance, so there's no need to add an extra button, therefore, you both save space and get better visual feedback.
 
I do not use drum maps all that much though I did try them - I usually do all my editing straight in the piano roll. I know some people like the Hyper Editor, but many believe that a proper drum editor would be better. I occasionally use it, but for controllers, not note data, or very rarely. If it's an integral part of your workflow, this could indeed be something that needs to be taken into account. For me, Cubase has always had the edge in that department. But for my needs, the piano roll is sufficient - I never really bothered w/ the drum editor in Sonar either. 

Rain
I've worked w/ a 13" for 2 years and while it wasn't the most comfortable thing, it was manageable. 

 
So I just missed out on an i7 iMac on craigslist - they were asking only $750, but someone scooped it up the same day.
 
In the even that Sonar X3 doesn't float my boat, I've been trolling for the cheapest Macs which can run Mountain Lion / Logic X.
 
Someone is selling a 2009 Mac Mini Core 2 Duo server with 2 500GB (5400rpm) drives with 4GB memory.  I'm wondering if this would do for song writing and home recording.  I suspect the constraint would be the drive speed.
 
Also, for bread and butter instrument sounds like brass sections, saxes, and basses, do you rely on samples which come with the ESX24?  I'm just wondering what takes the place of Dim Pro in Logic for these kinds of sounds?  There is no rompler included is there?  Is there an instrument plug that logic users gravitate toward for sounds which aren't included in the key, synth, and drum instruments included in Logic.
 
As I was writing, I realized that Dim Pro runs on the Mac - but then I checked, and it doesn't run on Lion or Mountain Lion - d'oh!!!
 

My own MacBook Pro is pretty similar in terms of spec - 2.7 GHz Core Duo 2, 4 GB and the obvious 5400 drive. For such a low spec machine, it actually performs pretty well. It always depends on what one means by song writing and home recording.
 
My projects usually end up between 40 and 60 tracks (more often on the 40-ish side) w/ EQ and compression all over the place, a few busses w/ reverb, automation. The bundled effects are very good (as I mentioned, the compressor is my favorite comp all around) and they also incredibly light on CPU. I'll often have a couple of reverbs running - Lexicon and/or Valhalla as well as Space Designer (Logic's own convolution reverb). But I also use Waves plug-ins and McDSP on occasion.
 
When mixing, I gradually increase the buffer size as I see fit when needed. I can't tell you that I ever maxed out my machine - not using Logic, anyway. Pro Tools' a different story. Most of the time, I have Mail and Safari running in the background, and iTunes quite often. And I didn't tweak anything - the machine is configured exactly as it was when I left the store.
 
When recording, I have the good habit of planning ahead which I guess serves me well. For example, I use only one pair of stereo outputs in Superior Drummer for as long as I'm in songwriting mode and working at very low latency - especially if I need to use Kontakt on top of that and and also need to monitor guitar tracks through amp sims and such. I know that Kontakt is highly unoptimized so I'll freeze that as soon as I can, and once I'm done recording and the arrangement is figured out, I'll have Superior Drummer use multiple outputs, and such... Maybe some people prefer to work otherwise, but that's my workflow, anyway.
 
As for the included stuff, I actually use them quite a bit, though I tend to not necessarily use them in a very orthodox way. When I'm not working on traditional drums/bass/guitar stuff, I'm more into odd soundtrack kind of things. For brasses, I couldn't tell, I just never use any. But there are definitely some decent piano, bass and such. I also have my own sample libraries - stuff I've created or instruments that I've converted into EXS-24 instruments.
 
If you ever get Logic, it's worth checking out Eli Krantzberg's EXS-24 tutorial on Groove 3.  Amazing stuff which shows, among other things, how quickly you can customize and/or create instruments. Worth every minute you spend watching it.
 
Here's an odd little something - intended to sound a bit like atmospheric DVD menu music - I put together for fun a few months back using only EXS-24 stock sounds and Logic's bundled FX. Nothing fancy and not actually mixed and too much reverb, but it gives an idea of some kind of sounds... 
 
http://www.youtube.com/watch?v=uKjlXwVCabI
 
 
 
 

I'm sorry to dig out this old thread, but I am thinking of getting logic. My question is regarindg the drummer, and especially the "follow"-function. Is the drummer indeed able to "follow" the selected audio track? or is it really a good-sounding idea that doesn't work in reality?