Reasons to be glad-
Competition is always good, and Sony is stepping up their game due to their position. They've also made the PS3 more affordable, and are making the PSN better. There are amazing first party games as well, due to competition. They will work ever harder to make the PS4 better also.
Reasons to be dissapointed (or mad. Ha ha ha. Get it? Glad/Mad?)
Sony was always competitive, and they have made an amazing piece of hardware that was offset due to the economic downturn and people being willing to buy and support a company that made a cheaper console that breaks, and conduct uncompetitive behaviors such as buying exclusivity. Making the PS3 affordable only made the console become worse, with backwards compatability lost, and USB ports going away. They were planning on making all those first party games before they were in the position they are in now. Now there's prospects that the PS3 will either be a Wii clone, that they will be less ambitious in what they produce, or that there won't even be a PS4.
I realize that the dissapointed section is much longer, and I admit that I'm a sole PS3 owner and that there's probably subconscious bias in play here. However you're going to be writing your own reasons anyway so it doesn't matter, please don't reply to me, but rather state your own opinion.