No it does not affect the read/write; I have Windows, Steam and some of the games I play on my SSD. I put some of the other games that won't benefit as much from the speed on one of the other standard HDDs.
The main downfall to SSDs at this point is that you want to avoid constantly writing over the same sector over and over because it will eventually kill the sector, though they are getting better at this with newer SSDs. We are also talking about many, many rewrites over the sector before it becomes an issue. So basically anything you plan on adding and removing on a regular basis would be better on a standard drive. Some manufacturers, like Samsung, recommend that you turn off restore point creation for this reason, since it will delete old restore points as space is needed for newer ones so it constantly rewrites over the same spots.. basically if you ever need to roll your Windows back to a previous point, you will not have one if that feature is turned off, if that's how you choose to setup your drive.