It fluctuates. If you look at the one-pager I provided to the committee, it's down slightly. But it does go down during the summer months, because if they're not lobbying or their undertaking has finished, they de-register. But over time it seems to be staying roughly at about the 5,000 mark.
Evidence of meeting #3 for Access to Information, Privacy and Ethics in the 41st Parliament, 1st Session. (The original version is on Parliament’s site, as are the minutes.) The winning word was investigation.
A recording is available from Parliament.