I get something that appears to be very similar with Numbers and Pages. When I use the Console utility to look at the log, I see a number of timeouts when the Versions software seem unable to find a file it is lookng for. An example is as follows -
07/10/2011 18:15:27.000 kernel: KLIF ERROR: scan for file /.DocumentRevisions-V100/PerUID/501/3/com.apple.documentVersions/F0C540D8-A381- 4F54-850B-EE3DC9E91559.numbers timed out, returning 1 as status
07/10/2011 18:15:27.000 kernel: KLIF ERROR: scan for file /.DocumentRevisions-V100/PerUID/501/3/com.apple.documentVersions/F0C540D8-A381- 4F54-850B-EE3DC9E91559.numbers timed out, returning 1 as status
07/10/2011 18:15:33.000 kernel: KLIF ERROR: scan for file /.DocumentRevisions-V100/PerUID/501/3/com.apple.documentVersions/F314D042-0608- 4C8E-B107-CA1ADBC2F5C4.numbers timed out, returning 1 as status
07/10/2011 18:15:33.000 kernel: KLIF ERROR: scan for file /.DocumentRevisions-V100/PerUID/501/3/com.apple.documentVersions/F314D042-0608- 4C8E-B107-CA1ADBC2F5C4.numbers timed out, returning 1 as status
I'm pretty sure that these are happening when the beachball is showing.
In some cases I get many more timeouts and the beachball is then visible for many more seconds.
Are you getting something similar?