Conclusions thus far:
Thunderbird tests have always had a low turnout when compared to Firefox tests.  Since 2007-06-08 was the first time Firefox and Thunderbird were separated into their own test-days and held during the same time, we are seeing the results more accurately than before.
Our highest results for number of testers always falls during school semesters, so the fact that school is out in the summer could be contributing to low numbers as well
IRC traffic is not a good indicator of a successful test day.
A low amount of traffic tells me that there were few issues, which is a good thing.
Looking at the charts as they stand, it is tough to extract any particular pattern.
It should be noted that all this does it show that the current situation isnt on a big decline.  We should still try to come up with ideas on how to promote the testdays better to get even more exposure.
The days where we had 30+ user participation were Seneca test days.
Based on these percentages, we can estimate that these percentages can be extrapolated from the combined tests as well.
Based on the "combined test" results, we can guesstimate that the following numbers may hold true for combined tests:
# of Testers # of Results
Firefox 7 266
Thunderbird 2 54
Compare that to the results of the last test day:
# of Testers # of Results
GranParadiso 1.9a5 Testday, 2007-06-08 5 346
Thunderbird 2.0.0.4 Testday, 2007-06-08 4 117
Results look positive!