I am a bit concerned about the mega server technology and the impact this will have on community building and also languages other than English.
As far as I understand the information about the system there will be just one server that creates different shards/instances of the same zones as every map can only host a given amount of players simultaneously in order to not hamper the players' experience. On what kind of shard I will be placed will be determined based on some kind of questionaire that finds out whether I'm more of a PVP person or a RP-player or what not.
Now, I assume there will be some sort of option to join friends' or guildies' shards in order to be able to play together (let's hope it will work better than GW2's join overflow did in the beginning

But what is about server-communities, like we know it from pretty much every other MMO out now? Will I be on the same shard every time I log in and thus be playing with more or less the same people over and over again, even though I'm not "friends" with them or in the same guild? Or will it be completely random within the limits of my playstyle as determined by the above mentioned questionaire?
To me the whole system, or my assumption of how it might work, appears to offer a more anonymous experience than I am used to from other MMOs.
Especially in connection with the PVP in Cyrodiil this is a huge concern to me (For PVE this might be negligible as most of that might be done solo or in premade groups of friends/guildies). Right now I'm playing GW2 and am in a guild which plays a lot of WvW. We are one of the most active and renowned WvW guilds on our server and also very active in the server's WvW community where we, or rather our commanders/raid-leaders, who are among the most liked of the server, are a bit of a brand name. But next to our guild's raidleaders thera are also a couple of other raidleaders that are active on the server's community-TS and that make WvW the unique experience it is; there are dedicated and experienced leaders online to lead you into battle pretty much 24/7 and this is what makes this kind of PVP great.
I'm holding high hopes regarding TESO's PVP in Cyrodiil, which appears to be comparable to RvR, or GW2's implementation of it - WvW.
But with the mega server technology I fear that it will be hard for raid leaders and regular players to find each other and get to know each other. In my experience people are less willing to follow unknown characters but if there are always totally different players on a shard, how will people recognize who's a good commander.
Furthermore, in the big picture of PVP, how will communication and alliances (cross-guild cooperations) work, if all the guilds on a given instance of Cyrodiil don't know each other (which is likely to be the case if you always end up in a different copy of Cyrodiil)?
I assume that strategy and jointventures of zergs will play a huge roll in this game's PVP. But how will we be able to know who's in charge of the zerg in the east if we have no static servers. How can we set up ingame communities with instable instances of Cyrodiil that are created whenever a certain instance reaches its player maximum?
In GW2 almost every Server had its own community TS to coordinate attacks and allow for structured gameplay without being in a guild or at off peak hours. How will it be possible to establish such community projects in a game without permanent servers? And to me this is paramount to such a type of PVP to be fun. How will this work in Cyrodiil if there are everchanging populations on each instance of Cyrodiil? I hope you understand what I'm getting to.
I'm really anxious that the mega server technology will lead to a fractioning of the PVP community (or rather make it impossible to create a factional PVP community) that will severely hamper this area of the game. Because without a established community this PVP will become rather unorganized because the players won't get to know each other if they are playing alongside different people every time they log on.
Also: How will the mega server work in regard to other languages than English. I'm from Austria and thus I'm used to playing on a German language Server in pretty much every game so far. How will that work if there is only one megaserver for Europe (or even for the whole world)? Will there be sub-shards dedicated to various prominent languages that are used to having their own language servers from other games (like German, French, Spanish; those are the ones I've seen in every game I've played so far.)? I''m asking because I know for a fact that a lot of my Germanspeaking fellows would be unwilling (or unable) to communicate in English and that this would definitely cut short their time in the game.