(That said, as commenters below correctly point out, Twitter, not Loren, owns the patent and gets to decide whom to enforce it against).
If something is patented, then no one else can patent it -- that's pretty clear and the patent office enforces it fairly well. If something is "obvious" (to one of ordinary skill) or if something has already been done, then it SHOULD not be patentable... but it is quite common for such things to be patented anyway. To be fair, it is unreasonable for the patent office to know about every thing which has ever been done, but still these things get patented.
Once a patent is issued, there is a presumption by the courts that it is valid. You can contest this, and use prior art to invalidate the patent but it will require litigation and will be VERY EXPENSIVE. You can "use it without fear" as long as you don't mind paying a trivial $100,000 or more in litigation costs.
I would be very pleased if someone knowledgeable about the practice of patent law would write in to correct me -- I really wish it didn't work like this -- but from what I have seen I believe that there IS a real danger that things which have been "released" wind up patented later.
I wish that were also true. In reality patents overlap hugely, and a line of trolls can form for the same feature. You have to spend the same 100k to show that another patent, issued earlier, also covered this idea, even if that patent was yours.
http://en.wikipedia.org/wiki/Defensive_publication http://en.wikipedia.org/wiki/Statutory_invention_registratio...
The Android Facebook app has this pull-to-refresh on its news feed - has for the last handful of updates. Pulse News also has used this same behavior for quite some time... It would seem that either these (and others) have been overlooked or the patent is indeed not being enforced at this time.