Firstly, to answer *gordysgirl*: No, just to make use of the PS3 you don't need anything extra.
If you have an HDTV you will need an HDMI cable
If he wants to play with friends, he'll need another controller
If you want him to be extra impressed, buy a blu-ray movie he might like.
Right, now the review:
The 40GB PS3 is essentially the same as a 60GB PS3 but it can't play PS2 games and it has 2 USB ports, not 4.
The USB ports aren't that important, you can buy a hub to get the extra ones, but the Backward Compatibility (the ability to play PS2 games) is a bit of a backward step (hence the 4 stars). Still, if you don't have any PS2 games it's unlikely that you'll miss this.
Is it worth getting a PS3? This is the hardest question, as it depends on what you already have and what type of games you like.
The Xbox 360 is cornering the market on games, well, apart from motion sensor stuff which the Wii does so well, and the PS3 so far hasn't seen too many outstanding games that give any reason to buy it over the 360.
However, now we have Warhawk, Uncharted, Rachet and Clank and Heavenly Sword with Gran Turismo 5 Prologue, Wipeout HD, Little Big Planet and tons more on the way. 2008 does seem to be a whole lot better for games.
Ok, so I could mention the hardware issues with the 360, enough has been said on this and hopefully Microsoft are putting a stop to it in newer models. But aside from this, the Playstation 3 is a better media machine. It has Blu-ray built in, a bigger hard drive, better streaming support (watching videos and music from your PC or Mac), can store your own videos on the hard drive and the menu allows easier navigation between all this media too.
The 360 costs £40 a year for online (especially now they've stopped you from playing demos on the free silver account). The PS3 is free. They say you get what you pay for, but the PS3's online has actually been very good. Ok, it doesn't have as good a friend system as Xbox Live, but it allows each game to use it's own style online access, which is sometimes good and sometimes bad. At the end of the day, though, it works.
The only real downside to the network on the PS3 is the lack of too many downloable games etc in Europe, though you can access the US site and download things from there.
The main reason you should buy any console is if you like the games. Second is if you're going to make use of the extra features (Blu-ray, media server etc). Hopefully this will make up your mind.
I have all three consoles, but I do love the PS3, it's very versatle, I love the games and the Blu-ray movies are fantastic too.