I just got online today and bought our ticket for the Eiffel Tower in July! Having heard the stories on here about tickets selling out immediately and people setting their alarm to buy them in the middle of the night in the USA (when sales started, Paris time), I really didn't think I'd have a chance at a reserved spot, but there still seemed to be a lot of availability.
Just thought I'd post on here in case anyone didn't know yet about the tickets being online!