So, I’ve been baking lightmaps for each object in blender then having to import multiple lightmaps to be used on a single object (many instances positioned aroud the scene) and this takes alot of time, and as soon as I make a change to my scene I have to go ahead and rebake the lightmaps. I found this http://unity3d.com/support/resources/unity-extensions/external-lightmapping-tool but it is for 3DS Max, do you think we will be seeing something similar to this for blender anytime soon?
You can bake them all simultaneously, just make sure all objects have a separate image to bake to in the UV image editor…or non overlapping UV’s if it all uses one map(make sure “clear” is unchecked in this case as well…) join the meshes(save first)…then bake…
-let me know if this helps or not…I did not follow the link…short on time.
EDIT: I checked it and you can do the same in blender…aside from GI, although you can use a touch of AO…
Hi Justin, I have been trying to get decent results for a few hours now, when I work on small objects with very few polygons, the lightmaps work perfectly, but I tried earlier to join objects together so that the scene was in about 3-4 groups (walls, ledges, props, etc…) and bake a 2048x2048 lightmap for each group, this seems to work fine, but when the camera is moved around the scene (in either unity or blender) I get some strange looking seams in the texture, I’m pretty sure this is something to do with how I’m unwrapping the uv co-ords, so at the moment the only way I can overcome this is to create individual lightmaps for each object which wastes alot of time and resources 
Heres a few screenshots of the seams:
In blender: (bad)
Rendered [blender]: (good)
Unity: (bad again)
I guess this is why I should stick to programming, and leave the assets to a real artist =P
it’s caused by mipmapping. for the highest mipmap stage your uvs are exact enough, but in the lower mipmap stages not.
…
i would like to see a better unwrapping method in blender for light mapping. one which works like the dedicated lightmappers like gile[s] do. you should be able to specify how many lightmap pixels you want per world unit and the unwrapper sticks to that resolution and automatically adds new lightmap pages if it runs out of space.
kakapo is 100% correct, it is mipmapping.
you can also bleed the edges out more…I don’t have the science of it worked out(guiltily lazy)but on a 1024 pow2 image about 8 pixels bleeding works for me…it depends how many mipmap levels are being referenced.