Well the first thing I noticed was, “Damn, that box is a lot smaller than my old PS3's box”. The next thing I noticed was, “Damn, this is a lot lighter than my old PS3.” The lighter, smaller PS3 is a little wider than the old PS3, but it's slightly wider girth is greatly overshadowed by the smaller height, the lower profile, and the overall sleek, matte black, design.
The PS3 sports a new 45nm processor, which, technical differences which I will not get into aside, requires less power. The power cord itself is just a standard unpolarized C8 cord (non-technical term: the same one the PS2, PS1, Dreamcast, SNES, NES, 3DO, etc all use), as opposed to the beefier C13 (aka IEC, nontechnical term: the one that your PC, monitor, and TV use) that the older PS3 uses. The cord is ungrounded, so I do recommend plugging it into a grounded surge protector if available.
The lower power consumption means a cooler unit which means the system is much less likely to fail due to heat than it's bigger, older brother. While overheating is much less of a problem on the PS3 than it is on the 360, many more people use the PS3 as a Blu-Ray player as opposed to a game console, and put it in tight spaces with little airflow. While I still don't recommend doing such, the PS3 slim should be able to handle it (but seriously, don't do it, make sure it is in an open area with plenty of space around it). The slim consumes less than half of the electricity of the 20gb and 60gb models.
The connectors are the same, Ethernet, Digital Optical Audio, Standard PS2 AV Connector, and HDMI are all there, and don't feel as out of place or hard to reach as they do on the older PS3's. There is no difference in audio or video quality between the fat and slim PS3, and such a difference is much more noticeable between different audio and television setups.
The slim boots up at about the same speed as the fat, and there's really no noticeable difference in performance between the two, and despite the fact that the 45nm cell should technically perform better, I noticed no difference in performance overall, whether from the HDD or from a Disc or in game. The buttons (eject and power) are actually buttons this time, which I heavily prefer over the older system's touch sensitive buttons.
The slim sheds its oft-fingerprinted covered, shinier, arguably sexier, glossy top, for a matte black top (however the sides and bottom are still glossy). The PS3 also sheds the old SpiderMan 3 font for a more sleek looking “PS3” logo. The feet that secure it when vertical have also been removed, basically forcing users to use the system horizontally rather than vertical. This isn't much of a problem, however, due to the fact that there is no heat exhaust at what would be the top of the PS3 if set vertical.
Overall the PS3 Slim isn't an earth shattering new console, nor is it trying to be, and it won't ever play PS2 games nor will it ever run Linux, but the fact of the matter is that it does what most people want, which is lower the manufacturing costs of the system such that Sony is able to drop the MSRP of the unit. At $299.99, it is the lowest price on a PS3, and doubles as the world's greatest Blu-Ray player, if you've been holding out because of the price, hold out no more, as I wouldn't expect Sony to lower the price anymore.