It depends on the game, but the major impact is going to be with mostly loading maps. If you have to load into War Z, or league game, opening applications, or your boot time. They will all be much faster.
I would go for it, you will see a huge difference in boot times (once windows actually starts to load), map loading times like darkness said, just make sure you have a secondary storage disk to keep everything on but the OS and games.
I'm considering upgrading to SSD, was wondering if anyone is using them and if the performance is worth the money and if they have a big impact on gaming.
What SSD would you recommend?
If you have the $ they are fantastic for loading. Consider the Seagate "Hybrid" they are about 25% the costs (just a little more than normal had drives) but have a limited about of flash drive built in); through computer algorithms they learn what you do all the time (like load windows, this hack or BF3) and those learned boot up or load times are as fast as SSD.
I have both SSDs and Seagate hybrid in my systems. The SSD rats 7.9 in Windows Experience the Seagate hybrid 7.7.
Samsung 830 Series 256 GB SSD is a good choice. I got 2 of them. You will see a huge impact on loading times.
But you should not use them as a download drive with xygb+ per day. That will shorten the lifespan.