Some things I find to be *FAR* more effective and time-saving than Photoshop, like the right-click on the picture for the menu feature. I was able to cruise through images and perform simple tasks in about one-third the time it would have taken me to do the same tasks on Photoshop (yes, I actually tried, I got three images done in the time it used to take me to do one).
In other areas, I am finding it light-years behind Photoshop. Some simple things, like editing a text-layer after it is created, are very straight-forward in Photoshop (you double-click on the layer and *bam* you're editing it) yet are nowhere near that easy in GIMP (I don't even know if GIMP *can* do it, that would suck).
Initial reaction: while a nice program for some simpler stuff, and it is off to a good start, I'm finding GIMP has a way to go before it can come close to Photoshop. But then, GIMP is free, which is a lot cheaper then the I-don't-know-how-many-hundreds-of-dolars price of Photoshop.