Even Apple seems to have admitted that Flickr is the best photo-sharing site on the web, and while its inclusion of native Flickr exporting in iPhoto '09 might have had an adverse effect on the Flickr-exporting iPhoto plugin of Scottish developer Fraser Spiers, it should mean nothing but good things for his iPhone app, Darkslide.
Formerly called Exposure, and available as both a paid-for and free ad-supported version, Darkslide is, frankly, the daddy of iPhone Flickr apps.
At its most basic, it's a portal to your own Flickr pictures; it's not as convenient as the Photos app, simply because it has to pull the images down from Flickr's servers. It does a superb job of caching thumbnails, however, so even if you're on an EDGE signal it doesn't feel agonisingly slow.
Tap an image once to load it full-size, or double-tap to bring up the info screen where you can add comments. From either screen, you can tap an icon to post a link to Twitter – Twitterrific, Tweetie, TwitterFon and Safari are all supported – email a link to the photo or open the relevant Flickr page in Safari on your iPhone.
It's much more than that, though; it gives you access to all Flickr features in a way that's optimised for the iPhone screen. It can use the iPhone's location services to show you those images on Flickr that are geotagged as nearby, and you can search the entire universe of Flickr photos.
Tap the More icon to browse your contacts' photos, look at featured photos, explore places, groups, sets, tags and favourites. You can comment on pictures, add them to favourites, and do all the forwarding stuff you can do to your own shots. There's no way to invite people to submit photos to groups, but we can cope with that.
You can also upload photos from your iPhone's photos database, complete with permissions, tags, descriptions and, if you want, embedded location information.
It is a superb, polished app, and while we'd like to see a way of authorising and toggling between multiple accounts, it's not something likely to bother many.
Try the free version, but consider dropping a couple of quid on Darkslide Premium if you're anything other than the most occasional Flickr user.