When I first read that Flickr was merging accounts with Yahoo! accounts, I thought it would be a good idea.
As of now, anyone can log in to Flickr using their Yahoo! ID. New users will have to use their Yahoo! ID (or create a new one if they don’t have one); older users can continue to use their existing Flickr.com account details to log in, or choose to merge their Flickr.com accounts and Yahoo! IDs together*. One note: Existing users will be able to keep their existing screen names on Flickr whether they choose to merge accounts now or not – you don’t have to change your name.
Now, based upon that, nothing would be lost and I’d just be able to log in with my Yahoo! account. However, not everything was perfect.
*Having said all that, there may be reasons why existing Flickr users would not want to associate their accounts yet: if you use API-based programs developed by outside developers, your favorite programs may not work until those developers update their programs to work with the new authentication API – many developers are already doing this, but during the transition process you’re better off to ask first and merge later!
An application I recently discovered, 1001, has already been updated. If you’re an iPhoto addict though, you probably use Frasier Spears’ Flickr Export Plugin for iPhoto. That plugin hasn’t been updated and authentication will fail if you merge with your Yahoo! account. I would suggest waiting this out.
Update: FlickrExport has been updated to 1.3.0b1 with support for the authentication. If you were waiting for this, you can pull the trigger on the ID merge.