It is fast. Just right tool for a quick peek. Slideshow works pretty well also. It just seems that if you drop a folder, it goes to slideshow mode, and when you drop a bunch of separate images, it opens them as separate images. Well... I can live with that. Caching seems to work nicely, though with hires images there are some responsiveness issues.
I wish it would show also embedded color profile in info window.
CMYK are shown negative, but that is quite common I guess...