• There's the option of anonymous photo hosting.
• I can distinguish between uploading and sharing images. On G+ if you upload an image you must "share" it then and there, or it's forever private.
• Useful annotations and titles. Roughly comparable, but I prefer Imgur's tools.
• Better album options. In particular, I can figure out how to add images to specific albums in Imgur. G+ is fucking opaque on this. Yes, I'd prefer to be able to add an image to an album from the image rather than by navigating to the album first.
• Share an image to User Sub or another gallery and enjoy the fun. Or just build up a library of images associated with my subreddit and/or blog (my primary use of Imgur).
All the fancy-schmancy image editing tools G+ offers? I don't use 'em. I've got The GIMP, it's good enough for me.