I have the Sony a100. I do not care about the features ... never use them.
I care about the image quality, which the Sony is pretty good at lower ISO. I spend most of my time with good optics (which you will find is a common opinion on in this group).
Sony makes some nice G glass ... and Minolta made some really nice lenses also (most were under-rated) ie Minolta Maxxum 28-135mm ... it is an awesome lens.
I'll echo what dxq says about the a100, but will add that the a200 is better at higher ISO than the a100, the a300 is better at higher ISO than the a200, and so on, and so on.
I have the a300 and find I can bump up the ISO to 800 and not notice any noise in the image, but when I go to 1600 it is noticeable, but not too distracting. The other good thing (again, as dxq mentioned) is that you can get Minolta lenses that fit the Alpha series. I have 2 myself (50mm f1.7 and an 85mm f1.4) This means you can get good lenses cheaper.
All this is moot if you want to get a Canon as Sony/Minolta are the only lenses you can swap mounting.
I only shoot at high ISO when I want the grain effect. I used to do this with film.
I never used high ISO film just to obtain higher shutter speeds ... my concern was with the image quality so I only used to shoot film slower than 125 ISO.
But that is just my opinion ... I see that many DSLR users on this board use higher ISO's for other than artistic effects.
FYI: most Camera manufacturer's have good glass. You can get some awesome Manual Focus lenses for the Pentax DSLR's (if you do not care too much for AF). If I had to start over I would seriously consider that.
I've seen some feedback on the net which considers the IS (18-55) to be optically superior to the non-IS predecessor, in addition to its stabilisation
capability. Whether it is better than the VR lens I don't know...
Perhaps there is comparitive test data at dpreview.com
Canon's range of lenses are more expensive generally than Nikon's I think.