Ok a couple points: First, if your goal is to freeze action, IS gives no benefit whatsoever. If, however you like the type of club shots where the photo shows movement (on the dancers part but no camera shake) then IS can be very beneficial. So, it depends on what your goal is.
By higher ISO's - what level?
I had been looking for 3200 ISO, but there are relatively few cameras which offer that, and most tests on ISO 1600 & 3200 are taken to simply show grain in a photo rather than how well it'll do in low light or fast action.
The noise level is the comparing factor. Exposure is the same regardless of camera (for the most part - you may see 1/3 stop difference between cameras). But, in general, ISO 1600, f1.8 and shutter 1/60 will produce the same exposure on a Nikon D50 as on a Canon 30D as on a Sony Alpha. So, if they're all exposed the same (and all stop the exact same amount of action) they then are compared based upon the noise level signature.
So, say you're a Nikon guy. The Nikon D50 has better noise performance than either the D70 or D200 at ISO 1600. So, it's a better low light solution (the D80 has yet to be really seen/ tested thoroughly). But, it doesn't have ISO 3200.
The Sony also has relatively poor high ISO performance (as compared to Canon or the Nikon D50).
The Canon lineup (30D, 20D, 350D) has ISO performance equivelent to the D50. It's newest camera, the 400D is just out so the jury is still out on how it's noise performance is (since it's a new sensor for Canon and still using the old Digic II processor).
So, back to the original question: If you want to freeze motion more than high ISO performance is more important or the use of flash - in either case, IS is not very useful. If you want to hand-hold at slow shutter speeds to get steady shots of either non moving subjects or to show motion of the moving subjects than IS is incredibly useful.