
You would never notice the difference between the two - all other things like RAM being equal - unless you were running a benchmark test. Since you buy a computer to do work and not run benchmarks, it is more of a marketing difference than anything.
If the budget is a concern, then take a look at a refurbished MacBook from Apple. You can save a few bucks, get the same one year warranty and the option to buy the three year AppleCare as well. Some users have reported getting free upgrades in either RAM or hard drive - or even both, but do not count on it. I would still hold off on ordering upgrades until the MB was received just in case you get a bonus.
I bought mine as a refurb back last July and it has performed flawlessly since then for me. I added 2GB of RAM and it runs everything I can throw at it.