When everything's sized down - noise grains become smaller and disappear.
If one regularly prints in huge sizes and requires your viewers to see them up close - ISO becomes important - but if you put 900x600 pixel photos online or in facebook... with an excuse that it's going to be vital for big printing and cropping for posterity's sake... try shooting in Small JPEGs - that would prolong your hard disk's life span... :sticktong
Well, most of us would realise that you don't print or crop all the photos except a select few, and the shots that aren't done for work or "tan jiak" purposes are shot for ourselves - and thinking that you need to shoot in full sizes would be quite costly in storage terms, and of course seeing them in 100% magnification essentially makes you see your photos as if they were printed in A0+ and bigger, placed at newspaper reading distance - of course, you can see noise...
But most of the time - for me when I see stuff in 100%, I'm reminded that I sucked at photography and there's still much too learn: unintended motion blur/OOF/focusing errors/ undesired DOF too - that happens for me at least...

:embrass:
In discussion of overexposing slightly as a High ISO work around method - I think it's important to consider that - in the process of getting a cleaner image - is it worth setting and potentially messing up your DOF or your shutter speeds to get that one extra stop of light to press the noise down?
Is a cleaner shot more important or taking a right photo more important?
Yes - the A700/850/900 indeed has a lot of highlight headroom - in the region of around 1 stop as compared to most brands out there because the sensor's tuned in that way to favor the highlights - I can pull down the exposure settings in a raw converter and have slightly lesser noise because when I took that shot earlier, more some of the intended shadow regions of my photo are now in the highlight regions, which has less visible noise. Then in raw processing, I pull them back down into the shadow regions.
To do that, for the same ISO setting - I can just increase my aperture or decrease my Shutter speed for overexposure... then pull down the exposure in Raw processing.
But that turns out that in practical application and from my experience - for me at least - is that - ISO ratings and noise are of the last concerns for me, and I'd usually increase my ISO when necessary because of two things: increasing DOF to include more stuff and also speeding up my shutter speed to Freeze Motion - both of them reduces the amount of light going into my camera.
I'd go for a little of that pixel inconvenience to get the shot that I need, then process out the grain and noise when necessary, and still get good prints after that.
To me, a well executed shot is more important than a clean shot.
That's my 2 cents' thought though. :angel:
As an after thought, even though it can be argued that some Sony DSLR models aren't good high ISO performers as compared to other brands, we are living in high ISO paradise if we compared what we have to the grain size we get from film. So yeah, I'm thankful, and only good things would come in the future yeah... So don't worry, be happy and shoot more. :sweatsm: