I don't know, maybe it's just me, but when I think processing power the first thing to come to mind isn't word processing... on the other hand, that additional 0.26GHz will definitely be noticeable if the OP plans to do any amount of audio/video encoding (even if just using iTunes and iMovie) or photo editing.
that said, I guess I tend to look at these kinds of decisions with a "buy the fastest/best hardware available at the moment" mindset, mainly so my computer will remain close to the cutting edge of technology for as long as possible (meaning I won't feel the need to go out and purchase a new computer every time another version is released)... in the end, though, your decision is going to come down to what you plan to do with your notebook- if you'll be doing any audio/video encoding/editing (or photo work in Aperture/Photoshop/etc.), I'd highly suggest going with the 2.53GHz version just because the extra speed will save you quite a bit of time in the long run. otherwise, if you'll be doing mostly word processing and browsing the internet or watching movies, then the 2.26GHz version should suffice.
*on a side note- if you're at all focused on performance, may I suggest investing in a 7200rpm HDD? the only reason I mention this is because I upgraded to one a few months back, and everything loads significantly faster, and at very minimal additional cost over a standard 5400rpm drive... just thought I'd throw that out there.