You may want to consider a refurbished unibody MB. They are on sale at apple.com | store | refurbished Mac. Before you go thinking it's like a used Mac, it's NOT. The refurbished is made to look as new before sent out. It comes with a full one-year warranty. It also is eligible for a three-year AppleCare warranty (which you can buy on eBay for a substantial discount of 65% off - or around $100). Most say these were open-box returns or was a problem which Apple fixes and then sells at a discount (why they charge 10% restocking fee for returned Macs).
I think the absolute best value for any Mac is the low-end unibody MacBook refurbished for $1099. Use the extra savings to buy 4 GB RAM from MacSales.com and a 100+ GB SSD for around $200 to $250 from newegg.com.
The speed difference is minimal upgrading from 2 to 2.4 GHz... The SSD will make a MAJOR speed difference in boot ups, app opening, and file opening. Also, the 4 GB RAM will make much more of a difference than the CPU upgrade.
Last few things to think about... you can buy the 2.4 GHz unibody MB refurbished for $1399... or if you really wanted to consider a new unibody MBP, but the money was too big of an obstacle, the refurbished unibody MBP is only $1699. If you ever want to do games, it has a dedicated graphics card. At that price, you could just upgrade the memory and SSD later down the road when you have the extra cash. Some people really like the MB for portability, and others really like the dedicated graphics and the much nicer display of the MBP. Anyways, the unibody MBP becomes only $100 more refurbished than the new 2.4 GHz unibody MB.
Don't fall into the hype the MBP is a "pro" model and you don't need that. The truth is whether you want a dedicated graphics card, a 15.4" display, a nicer quality display, or a more powerful computer, the only option is the MBP... as the MB doesn't come with any of those options. Those options really have nothing to do with being a "pro" of sorts. Other than "pros" made need dedicated graphics, but so do gamers and some application users. The dual graphics and extra power of the MBP will make it into one amazing computer once Snow Leopard is introduced.
Best wishes with your decision. All of the current Mac computers are really nice and would work well for most users... cheers.