[qazwsx]

Verse Servers can be used to share data between applications, they can either run locally or over the internet.
By downloading a build of Blender compiled with Verse, and a Gimp plugin, and connecting both to a locally run Verse server, I was able to have realtime updates of a texture made in Gimp in Blender,

Video: http://www.vimeo.com/5760951 skip to 1:40, before that I'm just setting up the server, Gimp plugin and Blender

Later on in the video, you can see realtime updates of mesh data from Blender into Loq Airou, a free, Verse-based subsurface modeler avaliable from the Verse website along with other free Verse-dependant software (including Verse server)

NOTE: Loq Airou is a very strange modeler using little to no keyboard shortcuts, relying heavily on context sensitive mouse gestures, if you wish to learn it, please read the manual: http://www.quelsolaar.com/loq_airou/manual.html

The Verse protocol allows the sharing of a wide variety of data between programs such as:
Subdivision surface geometry
HDRI Textures
Shaders
Transforms
Audio Clips/Steams
Lights
Scripts
Animation
(along with other custom data)

Limitations

Gimp:
Currently, the Verse plugin for Gimp only suppourts a single layer (the top one), however I have found a rather clunky workaround for this:
1. Create required layers and a top, unused one
2. Start up Verse plugin, connect and sync the image
3. Set this top layer to invisible and work on the other layers
4. When you want to update the image in Blender, use "Edit->Copy Visible"
5. Paste it and anchor it (or whatever the proper term is) to the top layer.
This top layer is then updated on the Verse server, regardless of if it's visible or not. However in my opinion, this can't really be thought of as realtime, if there existed a plugin that combined all visible layers and outputted the combination onto a seperate image every time the visible layers were modified, this new image could be synchronised with the Verse server.

Blender
Using a subsurf modifier (possibly others, I haven't tested them) on meshes when synchronising them with the Verse server causes Bender to crash. The crash shown in the video was possibly due to me adding, then duplicating a UV sphere (32 rings, 32 segments) before it was able to be updated in Verse and Loq Airou. Verse in Blender is hopefully going to be improved after the release of 2.5, the new back end will allow for easier intergration of new features.

Verse
As you may have been able to see, it is also possible to connect to a Verse server over the internet, this opens up possiblitys of collaborative modelling and texturing. However IMO, Verse needs to be updated so that backups, parallel versions of any peice of data and notifications about what exactly is being worked upon at a particular time are suppourted.

Links

Gimp: http://gimp.org/

Gimp Plug-in. http://users.telenet.be/blendix/verse/

Uni-Verse: http://www.uni-verse.org/Download-Files-rel-3.73.0.html

Blender 2.49a with Verse (Windows): http://www.graphicall.org/builds/builds/showbuild.php?action=show&id=1018

EDIT: Just to clear up any confusion, you run the Verse server on the same machine as you work on, connecting with both applications to "localhost".