Just to give you my input on the subject: (First off, I want to point out that there is not much difference between the actual performance boost a 2.53 i5 will give you in comparison to a 2.4 i5 that is identical in all respects with the exception of the faster clock speed)
I was facing the same dilemma as well and ended up going with the 2.53 GHz i5 for the following reasons: I originally ordered the 2.4 with my student discount and upgraded from the 320 GB HD to the 500 GB HD @ 7200 rpm, and got the HI RES Glossy screen. I then realized that because the 2.53 GHz already comes with a 500 GB HD (only 5400 rpm but it is still not as expensive to upgrade to the 7200 rpm in comparison to the 2.4 GHz) it is only an extra $60 to go from a 2.4 to a 2.53 with identical specs everywhere else (i.e. 500 GB HD @ 7200 rpm, HI RES Glossy, etc.) with my student discount (Note: I am not sure if the price difference holds if you are not eligible for a student discount). Given that I want my new computer to last as long as possible I could definitely justify spending the extra $60 for the 2.53.
[EDIT:] I just checked the regular Apple Online Store and without the student discount I would have spent an extra $107 (as opposed to $60) to upgrade from a 2.4 to a 2.53 with identical specs everywhere else. This is still not a lot but if you are not eligible for the student discount the choice is less clear.
The moral to be derived from my particular situation is that in the education store (and once again I must re-iterate that this might not hold if you do not have the student discount) the biggest reason for the difference in price between the 2.4 and 2.53 comes from the difference in HD specs. If you are planning on purchasing your 2.4 as a CTO from Apple and upgrading it to a 500 GB HD you are probably going to find, like I did, that there is not a whole lot of difference in price between the 2.4 and 2.53. And if you are trying to "future-proof" your new MBP like I am you can probably justify the extra price for the 2.53.
On a related note even though I would never be able to exploit an i7 2.66 to its full potential (given what I use a laptop for) I still wanted one but, there is a $150 difference between the i5 2.53 and a $210 difference between the i5 2.4 (even with my student discount). This difference was too much for me to consider the i7.
I hope this helps.
