Agreed. I was thinking about this the other day and I think a Pixoto app for Android / iOS would be a great convenience. Image dueling may be a little difficult due to small sized screens on phones, but there are ways around that.
The app would be more used for editing profiles, image dueling, or just browsing through photos. Uploading photos via smartphones, while not impossible, may be a little tricky. Perhaps through dropbox? Photos could always be uploaded into the instagram/mobile category directly from the phone though, for obvious reasons. Hopefully something is in the works already.