As far as I have read these merges mean the following;

Your guild will remain in tact, including members.
You will be placed in the same realm as you were previously.
GW will be wiped clean ( does that mean that the top 10 servers will change to the new system or won't be merged?).
You will still have the option shown as being the server you previously inhabited but both are directing players to a same spot.
Name changes of guilds can occur and when they do you get a free change possibility.
(if any of the above is incorrect, please let me know.)

Did character names change at all? Or did they not have any similar names around?
Have there been any bugs?

I am very happy Tynon is trying this out and look forward to more news about the subject!