Do you mind the Top-loader disc?
Getting rid of the USB ports is a much bigger deal than the PS2 backwards compatibility. In the first couple years of PS3 life cycle it was more important to play PS2 games, but now many of those high quality games are either in HD collections or available for digital download. I still have my copy of NFL Blitz 2003, but since a new version came up for download on PSN, I've been trying to sell the only PS2 game I've played in the past 3 years.
Only having 2 USB ports is a killer for people who either like playing PS Move games, using a PS2 controller, or like playing with a headset. It's one of the reasons I will probably cry if my fat PS3 dies and I have to buy an adapter to expand it to 4 ports.
The top loading does seem cheap, and much more likely to get dust in it, but going cheaper is necessary since Sony will be selling these for the next 10 years. Think about how people are still buying PS2s over 6 years after PS3 has released! On the same note that says that more dust will get in the disc tray, you likely can just blow into it or use a cleaning wipe.
I do really like how they include a 500GB hard drive with the $300 version. The PS3 "only does everything" and needs a bigass hard drive to store all the photos, movies, demos and games you can download/transfer without thinking too hard about it. People who have never upgraded their hard drive won't understand, but I only have about 20GB available after installing a 500GB Seagate drive over 2 years ago.
I know a few people that have had the disc slot fail on there PS3s and have had to tear the things apart to get their games out of the disc drive. With the top load mechanism there is no worry about getting the disc locked into the PS3.
On most systems top load disc drive is more reliable. The fact that it slides to the side means that it can still fit into most entertainment centers. However you will still need to have room to reach your hand in above the PS3 to place the disc into the PS3 SS (SuperSlim).
Over all I like the look of the new PS3 SS but I like the slot load drive of the older PS3 S (Slim).