I would imagine, when people are allowed into the hotel at the torch, or the swimming pool.

This structure is between Villagio and Khalifa stadium.

What I understand of the Torch is that it was built at the highest point in Doha, hence from anywhere in Doha it is visible..... have not checked this out.

Also agree with rayyz about the Salam towers view, The Shaheen restaurant at Sheraton, The top most restaurant (forgot the name) at Ritz Carlton.... I think from there you can see the Pearl being constructed.