Backwards compatibility with PS2 games (all versions play PS1 games), larger HDD, card reader, and two extra USB ports. All worthless in my opinion.
1) Unless you have a bunch of PS2 games with no PS2 to play them on (which is doubtful), that feature is pretty much worthless, especially considering it's only software emulation (something that can be added later with a firmware update, should Sony decide to do so, and only plays about 85% of PS2 games).
2) Card reader - some have a use for it, most don't. I'd prefer to just use an external HDD. In my case I took an old 40GB IDE HDD, put it in a USB 2.0 enclosure, reformatted, and bam an external 40GB. Or you can get an external USB card reader for cheap if you REALLY find you need it.
3) Two extra USB ports, big deal, there's a nice USB hub (I think by Rosewill) with 7 USB ports that you can buy for (IIRC) about $25 that seems to match the PS3 very well.
4) Larger HDD, another "big whoop." It's VERY easy to upgrade your HDD (they even give you instructions on how to do it in the manual) and for less than the extra price of the 80GB you can have a 120-160GB HDD.