I just installed Snow Leopard on a MacBookPro, and installed some other software (adobe, cinema4d, etc...) just to test it before compromising a general update on daily work computers.
I installed VW 2009 sp4 and it opened ok. I was able to draw some simple 2d, change views, everything basically ok. I was able to open a big file and move around, save, draw some 3d, render in opengl, also ok. In fact i felt it faster an more responsive, snappy.
VW crashed always when importing a dwg
VW crashed once after a boolean -substracting two solids- (but it also crashed there ocacionally in leopard)
It was not an exhaustive test, just a 20 minutes going around, and i will not upgrade to SnowLeopard in my other macs until NNA ensures a fully compatible version of VW, but at first sight, its not as bad as I thought after reading the technical bulletin stating the stability concerns...
MacBookPro, 2.9 Intel Core 2 Duo, 4Mb Ram, Nvidia GeForce 9600M GT 512MB, Mac OsX 10.6
Vectorworks Architect 2009 SP4