Just searching through our production systems, the largest one had 862 cron jobs (across all users, the largest single one, root, is 117), and it doesn't particularly break out in a sweat with that many.
If you start 60 jobs every minute, 24x7, and they all take two seconds to complete, then you'll probably end up in a world of pain. But, as long as the workload balances out (with quiet times and such), it should recover. Keep an eye on system loads during the peak times (CPU%, disk I/O, ...) and worry more about that than the number of actual jobs.
This question is akin to "How many processes can I run before getting into trouble?". The best bet is to try it, since it depends on your system. Cron itself has few limitations that I've found but, if you're trying to schedule tens of thousands of jobs, you're putting more of a strain on it than I ever had.