Pros: Still works; updates keep it current; does pretty much everything
Cons: Big, hot, not stackable
Even now, I'm finding new uses for the old machine. I recently purchased an Amazon Kindle Fire HD (the new entry-level one); the PS3 is one of the few devices that works with the Amazon "X-Ray for Video" feature. Run the Amazon Instant Video app on the PS3, then bring up the video you want to watch on the Fire. "Send" the video to the PS3 and you can now use the Fire as a "second screen," displaying IMDB data on the actors, characters, trivia, music, etc. and letting you play/pause the video which displays on your TV. This is an ancient device, by electronics standards, supporting an almost cutting-edge feature.
I'm not a big gamer, but I do enjoy some racing simulations and puzzle games. When my son visits we race head to head with GT5. Besides that, I play Blu-rays, listen to music and watch videos served from networked computers and storage around the house, look at photos with the family, watch streaming video. It's a versatile, reliable, and constantly useful device which seemed expensive when I bought it, and now seems like the biggest bargain ever.
No compelling reason to switch to a PS4. Sony's policy of continuing software/feature updates combined with a user-replaceable hard drive deserves praise.