SIMGallery is one of those extensions that, upon using, simply "WOW"s you. It is so packed with features that it's really difficult to review it properly!
There are many things I just LOVE about the component. From the tagging feature (that is wayyyy better than JomSocial's) to the VERY intuitive photo browsing. My users are REALLY impressed with the profile picture management, especially the part where you can simply use your webcam to take a photo and upload it immediately. Allowing users to upload multiple profile pictures to choose from, and the ability to select any photo to become their profile photo is also very useful. In fact, they even thought that I somehow got the script from Facebook! (SIMGallery *really* works exactly like Facebook)
I really recommend everyone to take a look at the demo on his site, and be prepared to be amazed. Can't wait for the next version and see what new goodies there will be!