Flickr is the best of the commercial photo-hosting websites. My two favourite features are that it stores the original full-resolution files, and it allows granularity in dates (e.g. month, year, or 'circa').
But things shouldn't be left only on Flickr, and so I want a way to pull photos into MediaWiki, and manage them there.
The first part of this was to convert FlickrAPI to use extension registration, but on further thought it seems that an import-only extension is a better way to go (I like the idea of a wiki being self-contained, and so linking directly to Flickr images feels wrong). I've started work on a FlickrImporter extension.
The other thing I use for backing up my Flickr photos is flickr-cli.