As per a conversation with Crell in irc:
Apparently during his work on database abstraction he's running into issues where exceptions are being thrown by his tests and the data is being lost, rather than captured and printed in the simpletest reporting. I think this has some crossover with http://drupal.org/node/214028
I think we should be breaking up tests by method, and executing each method within a try block, in the event an exception is thrown we should be printing $e->getMessage(), $e->getLine(), and $e->getFile() into the reporting.
If I can get a couple +1's on this i'll put it together. Opinions?