I'm not too keen on using noise reduction in post - I just stick with whatever amount the camera is doing on its own in jpeg, or using the same preset in RAW. I too like to use high ISO quite often, and routinely shoot to ISO6400 as needed. My #1 reason for high ISO is available light photography, which I prefer in style and atmosphere to flash. #2 reason would be shooting wildlife in low light conditions, where there really isn't an alternative (750mm is too far for flash!). #3 reason is for occasional night handheld shooting, which can range from scenic snapshots to street-type shots, where tripod and slow shutter is not an option.
BTW, what's interesting about this IDC update is that it appears to essentially be using the same processing algorithms that were created for the A500/550 cameras, as they had already significantly improved the high ISO noise reduction with regards to chroma, and producing a much more pleasing fine-grain lumi noise that preserves reasonable detail.
Some high ISO examples of various types I've shot with my A550:
High ISO and a fast prime are fairly necessary to get shots at Disney World in their dark rides - this was ISO6400 at F1.6:
My cat moves around like a spazz, so high ISO is mandatory in available indoor light. This at ISO3200:
This was just one of those 'have to have it' moments - I don't know why I wanted to take this shot, but I did - the boat was escorting our ship out of port, moving at speed, in complete moonless nighttime blackness - only the lights from the boat itself were visible. ISO6400 let me eke up to 1/13 shutter, just enough to make out the boat details among the lights:
Sometimes, it's just a spontaneous shot...like when I had been out shooting star shots in the front of my house, and decided on the way back to take a quick handheld of my house since the tripod was all folded up and I didn't feel like setting it all back up again. ISO3200 is clean enough to get away with shots like this:
None of these have post-processed noise reduction, but the NR applied in camera is pretty much what you get with the new IDC version...so it may give some idea of what to expect. To me, photography is just fun, and I don't like having limitations with it - I try all kinds of photography, from landscape and wildlife to portrait and action...and I like to try slow-shutter night shots and handheld high ISO stuff.
Sony DSLR-A580 / Sony 18-250mm / Minolta 50mm F1.7 / Sigma 30mm F1.4 / Tamron 10-24mm / Tamron 200-500mm / Tamron 90mm F2.8 macro / Minolta 300mm F4 APO
Sony NEX5N / 18-55mm F3.5-5.6 / 55-210mm F4-6.3 / Pentax K adapter / Konica K/AR adapter / bunches o' Konica & Pentax lenses!