Picasa is simple to use, generally friendly with other pgm interfaces, and you can import anything into PowerPoint as long as you have saved it in the correct format.
I find Picasa is a bit of a space pig, and can be a tidge idiosyncratic about "grabbing" pictures - it saves pictures multiple times, ie., every instance of the same photo, placing them in folders according to where it finds each instance.
Aside from that, Picasa is a piece of cake to use - easy interface and turns out a good product. I use it in conjunction with PhotoShop, because some of the Picasa controls are easier to manipulate.
It is free, online, and you can collapse the "faces" and albums" functions (though you can't get rid of them), if you find them as annoying as I do