From one geezer to another ...
The newer Blackberry's are 3G enabled for faster browsing. I don't like the touch screen Blackberry Storm (or any touch screen moby period!) and would sacrifice a smaller screen for a proper keyboard but that's personal preference.
Also, the standard new interface on the Blackberry Bold that shows the 5 icons at the bottom isn't my cup of tea either but you can change the theme easily enough. The camera's on the newer models are better too and some people seem to love the new trackpad thing instead of the traditional rollerball (I prefer the rollerball).
Other than that, the same bulletproof BB stuff you have in the 8310 is all there in the newer models.