CD lense cleaner. Is it necessary ?

If it is used in a smoking environment I should certainly recommend it. Even if you don't know the history of the player I should do it anyhow. In case of strange behavior or problems it's one of the first things to do.
I have used a cleaning disc myself, but prefer taking of the hood of the cdp and clean the lens directly with a clean cotton swab -- you can clean your ears with those, helps a lot too, now and then ;-)
Be very very careful!!

Yes many manufacturers {Marantz for one} are recommending to stay away from those self cleaning discs. My answer is somewhat a combination of the first two posts. If your machine is exposed to dust or cigarette smoking over a long period, Pop the top and clean it yourself. Its very easy to do with most machines. If your CDP is in a non dust attracting smoke free enviorment, and you can honestly say you have never heard any sound degradation, then I would leave it alone.

I can hear the improvement after cleaning even on boomboxes. Dust accumulates in time. What kind of nonsense is this not to clean the lense? True, one has to be careful not to scratch it and to use an appropriate fluid.

I was ready to get a new DVD video player since certain discs were not being read by it while playing on other players, until a friend suggested I try the Radio Shack cleaning disc.
They had several to choose from. One was for DVD and CD palyers one was for just DVD. It was hard to see what the differance was but I purchased the one for DVD.
It worked very well and all the discs that wouldn't play now play perfectly.

If you live in a dusty environment, lens cleaning is mandatory. The dust build-up over time will definitely affect the sound. I have never damaged anything using the cleaning disk. You are more likely to damage something using an anti-resonance mat.

This is what "What HI-FI" has to say about your question in a section of their web site re: system maintenance...

...CD player lenses can also get dirty, especially in smoky or dusty environments. If your player starts to skip, you can try a cleaning disc - these usually have little brushes on them to sweep the lens clean, and are sometimes used in conjunction with a drop of cleaning fluid provided. They usually do the trick - if not, older players may need to go to a repairer to be opened up for a clean.

audioengr,
How can you damage something by using an anti-resonance mat? This is the first I've heard of this. Does this happen often? Thanks.