I'm still discovering new features of my PS3, after owning one for about 4 months. Some features I am aware of, but can't fully take advantage of. For example, I can't play any games in high-definition because I do not yet own an HD-TV. Likewise, while I have rented one Blu-Ray movie, I don't really see the point until I have a better TV. After all, without an HD-TV and an HDMI cable, the picture doesn't really look better.
What I've recently discovered about the PS3, though, is an interesting little feature: the Remote Play ability to control your PS3 via a PSP. I don't know how many people actually own both of these devices, but their connectivity is pretty simple and, well, powerful. First you connect them via the USB cable, which basically registers your PSP with that particular PS3 system and lets them recognize each other. Then there are a couple of ways to get into controlling the PS3 with the PSP. The slightly more convoluted way is to power on the PS3, go to Network icon on the XMB, and set it manually to Remote Play. Then, do the exact same thing on the PSP and you're all set. What I think is the cooler way is to change the PS3 settings so Remote Play also enables a remote start. This way, if your PS3 is in standby mode and the TV is in use, you can turn it on and use it with the PSP without messing with the TV.
Ok, so you can turn on the PS3 with the PSP. What else can you do? Perhaps one of the best uses of this feature is watching video clips stored on the PS3 remotely. This is pretty good for me too, since I'm not really losing much quality because I only have a standard-definition TV. Less significantly, you can use the PSP's mobility to watch videos away from the living room (or wherever the TV is). I'm also not certain, but I believe a handful of PS3 games allow for Remote Play. I'll have to check on that.
I also love that PS1 games, as well as at least one PlayStation Network title, can be played remotely. I tested PixelJunk Eden, since it's the only PSN title I own, on the PSP. While it doesn't work nearly as smoothly or look as good as on a TV, it's still more than possible to play it. Remote Play is also particularly well-suited to playing old PS1-era RPGs. I've had an itch recently to play through Final Fantasy IX, which is one of the few Final Fantasy games I've neglected. The slower pace and lack of intense action makes games of this type easier to play remotely than more fast-paced games.
Which brings me to my biggest complaint about Remote Play: there is a noticeable lag when accessing the PS3 through the PSP. Since you're not using the PS3 directly, but instead over a wireless network, it's inevitable that a little of the finesse, of the near-instantaneous response time will be lost. This is why games like FFIX work so well remotely, while a 2D fighter might be a little more difficult. A second minor problem is that the PSP battery life was short enough on its own. By using the wireless connectivity constantly during Remote Play, it just runs down that much faster. So you can't expect to use this feature for an exceptionally long stretch of time.
This is a nice little addition to the PS3's feature set. It feels more useful than other handheld-console connections (such as GBA-GameCube), perhaps because the feature is not tied to a specific game. Instead, you have full access to the PS3, and can do pretty much anything you would normally. It's also very advantageous if you live in a household where the television is shared. If someone is watching a TV show, but you really want to play through the next dungeon in FFIX or start downloading a new demo, you can still do it peacefully. Just set the PS3 to standby, boot up the PSP, and go to town. Remote Play may not be perfect, but in certain situations it feels just right.