That's an old, cached message. There is no 300mb limit anymore.
Large scale deploys are hard. Give them some time for the dust to settle before over-reacting.
Despite the wrong execution on the process of rolling out the changes, the 1TB free is real.
So, can Flickr be considered as a reliable backup solution for my photographs?
The pricing changes might not be great (I won't attempt to evaluate them -- I'm not a Flickr customer nor in the target market whatsoever), but the 300MB cap claim is silly. You say it yourself: it's only been a few hours since they made this announcement at all, and they just removed that cap from the terms of service. They'll get to removing the technical restriction soon, I'm sure.
C'mon guys. I'm as big a fan of rage-fueled blog posts as anyone else, but can't we give them even a little breather before breaking out the pitchforks and torches?