Conclamo Ludus

For those of us who don't change our own oil:

At the 20 min. Oil Change places, when they are trying to sell you all those engine cleaners and radiator flushes, etc. Are these things really necessary. If so, how often? It seems like every 3,000 miles they are trying to push all this stuff on me. How often do you use these products if you do change your own oil?

I'm not a big car guy, as far as maintenance goes. Any advice would be appreciated.

Thanks.