Along the horizontal bar (New posts, Private Messages etc.) you can choose Community, then Member List. On the right, there's a Search feature. Clicking advanced search allows you to search on a bunch of various criteria, one of them is join date, but I can't seem to get that to work. (I still get ALL members showing up even though I try to search for those who joined after April 10)

What I can do is just go right to the bottom of the advanced search and chose "sort by join date" and "descending". Then, all the members will be listed from newest to oldest. I just went 3 pages in, randomly, and clicked on the 90th person's profile, and I can see that his/her join date was April 13. I'm not sure why the search feature isn't working for me, but at least I can rank people by join date and then verify that the 150th person joined on April 10, but the 180th person joined on April 8. I could keep trying until I found the exact count. But yes, as of now, it's over 150 people since April 10.

Also, Filark could have just happened to notice the total number of members on April 9 or 10, and just be comparing it to the total number of members s/he notices now. But if you really want to know such things, there are ways.