Not at all. Few games, if any, utilize hyper threading. Not only that, you're paying more for slightly higher clocked i7-2600k which can be achieved for free by overclocking it yourself.

Just overclock your i5-2500k to 4GHZ, it's a relatively easy task with even some of the lower end after market air heatsinks. Something like a Hyper 212+ will get you to 4.5Ghz, personally, I'd just overclock to 4GHZ and call it a day...more than enough power for anything you need.

yeah, its not a worthy upgrade UNLESS

you heavily use heavily-threaded applications such as rendering and video-editing

I agree with the both of them. It depends what you are using your computer for. If you are using it for things like video editing, rendering, 3D Design and things that take advantage of hyper-threading etc, you're best bet is getting an i7 2600k and overclocking it some more. On the other hand, if you are just gaming, the Intel I5 2500k is more than enough. Infact, The I5 2500k and the I7 2600k perform pretty much the same in games. The only difference is the hyper-threading abilities. :)

Just for gaming, no.

Man, guess I shoulda went with a cheaper i5 instead of going for the i7

Core i5 2500k vs Core i7 2600k @ AnandTech:
http://www.anandtech.com/bench/Product/288?vs=287