One way of moving a beta world to MC 1.0

(This is not meant to be an exhaustive guide, and I'm sure there are many other suggestions on how to do it as well. This is just a brief description of the tools we used, and the results)

Yesterday we took down our small private server with the intention of keeping the core of our existing world (we started in MC beta 1.3) but besides that running a new v1.0 generated map. We're quite happy with the results. We've so far only done this in the main world but will do something similar in nether as well.

I strongly recommend backing up your world after EACH step below, you don't want to redo everything if a specific step doesn't turn out as expected.

1) Copy your world from the Bukkit directory into Minecraft so that MCEdit can find it. Load, and find the smallest bounding rectangle that will fit the things you want to keep but still not delete chunks too close to existing structures. In our case this turned out to be an almost perfect square at around 1000*1000 blocks.
2) Select that square, go into Chunk mode and Prune everything else (you ARE on a copy of your map, right?)
3) Now select all and Cut. When asked if you want to replace the cutout with air or delete the chunks I choose to replace with air, so that I easily could see in the next step where to re-place the cutout.
4) Paste your cutout, which will now give you the option to Rotate. We had several structures built to catch the morning and evening sun and wanted to keep those vistas. I think it should be the same amount of rotates for everyone, three, equating to 270 degrees (I didn't see the option to choose rotate direction in MCEdit). NOTE: This WILL affect your rail switches and nether portal placements!
5) Since the ocean has been lowered one block in 1.0, newly generated chunks will cause non-traversable waterfalls when aligned with your old ocean. The solution is to blame Global Warming Still in MCEdit, select the top ocean block layer all over your map (1000*1000*1 in our case) and Replace water with air. Call it evaporation. Yes, you will need to redo existing docks etc if you have them.
6) If your world wasn't a perfect square, you now likely have air chunks outside some edges after the rotation. Select your world again, align to chunks and Prune. Save. This is now a 1.0 "compatible" version of your old core world. Make a copy, run it in single person (or on a test server) and make sure everything looks ok.
7) With the map back in the server, install VoxelSniper and WorldEdit. This part can take as much time as you want to give it (in our case, a few hours). Traverse the edges of your old world, which will cause the creation of new chunks, and blast the ugly boundaries with VS melt/random erode. Fix any resulting running water with WE fixwater.
8) For good looks, traverse the edges again, this time using VS overlay and "paint" the bare rock you got in the step above with grass and/or sand.
9) Fix all rail switches :/ They're now inverted compared to before ... (if you rotated your world). Also, your previous nether exit portal will now appear in a different place (again, if you rotated).
10) We haven't found a ten yet, maybe we will.

If this helps anyone, it was worth the time writing it. Have fun!

edit: Also, if you're using Stargate by Drakia the rotation will screw up its database as well. Just knock off the signs and re-place them to re-register the gates.

The image below is from MCEdit, in between steps 6 and 7. The effects of the drop in water level clearly visible:

 

Thank you for this mini howto!

I hope also a plugin dev will create a simple import plugin like it had been in the past, because if i must do this action my multivers server....13 maps at moment...omg...

 

I guess we were lucky, because we didn't plan for it, but saving a core not much bigger than ~5-600 block radius seems to make sure that you will get the three Strongholds in new chunks just outside it as well.

If you need to save a bigger core from your old world I'd suggest moving it at least 1200 blocks in one direction away from spawn.

edit: blutherz - thank you. Many of the steps I outlined could be added to MCEdit as one single action. Not sure smoothing out the edges should be automated too much though.

 

With the RB finally out I guess more people will try to move their old maps to 1.0. I'd like to stress the importance of the distances above if you want Strongholds, and also add that we indeed did the same operation (much simpler, only cropping needed without rotation) in the Nether as well. It seems the actual terrain generation hasn't changed there which meant that the borders look just fine and we actually got a nice Nether fortress just outside an excavated area with player built structures.