The main announcement, explanation, and discussion thread is over in the Poser forum.  While OBJ can be used by just about anyone, I expect the first and heaviest users to be Poser users.  But if you get some use from OBJs with XSI, Maya, MAX, Blender, or anything else, then join in and let me know!
Mac

Thanks for the heads up!
 
Ultimately, now that Max, Maya, and XSI are all Autodesk products, and all support FBX, I want to shift to FBX file processing.  But I just found the PC2 file format, and it's pretty straightforward (very much like MDD), so I may hack in a PC2 exporter for the short term.
 
For anyone interested, the PC2 format can be found here:
http://www.footools.com/plugins/docs/PointCache2_README.html#pc2format
 
Here's the short synopsis (I am just going to blindly assume that 'int' is 32 bit and that byte order is little endian):
 
.PC2 File Format:
You can create or modify PointCache2 files by hand using the following file format. The start of the file is a header containing:
 
char    cacheSignature[12];   // Will be 'POINTCACHE2' followed by a trailing null character.
int     fileVersion;          // Currently 1
int     numPoints;            // Number of points per sample
float   startFrame;           // Corresponds to the UI value of the same name.
float   sampleRate;           // Corresponds to the UI value of the same name.
int     numSamples;           // Defines how many samples are stored in the file.
 
Be sure to check the version number. If it isn't 1, then don't mess with the file, as the format will change in the future.
 
Following the header, there is a straight dump of all the cache samples (which are snapshots of all the point positions for an object). Each sample is stored one after the other as a flat array of x/y/z floats for each point (so each sample is (numPoints * sizeof(float) * 3) bytes).