The most well known developers of Bitcoin have raised important issues regarding the long term viability of the Bitcoin network, and the various solutions proposed going forwards. Due to the lack of consensus, this has resulted in a great deal of fear and uncertainty in the user base.
The code which powers the Bitcoin network can be found here: https://github.com/bitcoin/bitcoin This code has evolved as long as Bitcoin has been around. But the debate over the block size limit and how to manage it has caused some of the best known developers to set up another client for bitcoin, here:
https://github.com/bitcoinxt/bitcoinxt Edit: The bitcoinxt github has existed since 2014, but it's only now over the max block size debate that Gavin Andresen has leant support to it
The former is now referred to as "Bitcoin Core", and the latter "Bitcoin XT". For the time being, you can use the same wallet with both bitcoin clients, and they run on the same network. From the XT github README:
"Bitcoin XT is more experimental than Bitcoin Core, and has a strong emphasis on supporting the needs of app developers and merchants. By running it you not only provide additional services to the network but help build confidence in the implementations, contributing towards consensus for inclusion in a future version of Bitcoin Core.
XT uses the same data directories as Core so you can easily switch back and forth."
If/when the two change dramatically enough, that may no longer be true, in which case the network will 'fork', resulting in a new Bitcoin XT network incompatible with the Bitcoin Core network, which would require different wallets. But the important thing to bear in mind is that if you have a backup of your current wallet now, you can run both clients/networks - essentially, if you have 1 Bitcoin, after the fork (if you have today's wallet backed up) you will have 1 Bitcoin, and 1 'BitcoinXT', each with independent values based on their popular adoption. As Bitcoin is currently by far the dominant cryptocurrency, it is extremely unlikely that both possible future versions of Bitcoin would either cease to exist or lose all value, and the developers are doing their best to avoid a fork and reach a common solution to the necessary evolution of the technology.
So please, try to keep the debate about this big news relevant to the facts and keep in mind that as with all Bitcoin news, many people will attempt to use the news to manipulate those without full knowledge of it to affect the price in their favour. We need discussion, not panic.
Addition: luke-jr has responded here http://www.reddit.com/r/Bitcoin/comments/380nlv/the_bitcoin_core_vs_xt_debate_and_necessary/
For a lot more detail and Q&A check the bitcointalk thread here I started with the same text as above: https://bitcointalk.org/index.php?topic=1076316.0
And for more about the author, as well as other recent Bitcoin news, see here: https://www.cryptocoinsnews.com/ccn-podcast-episode-4/