Ok, there have been some odd speculations in here, let me help:
1) A newly added address needs to be absorbed into the system, don't ask me if it needs to float off to icloud or whatever, or even how long to wait, I don't know for sure, an half hour seems to work for me, your millage may vary....
2) Be sure your contact has a first and last name - even if you need to make it up. As an example, I have my local walmart stores listed as first name Walmart, last name [the city it's in] (I'm rural, in a larger city than mine, you might make it the street it's on instead of city). I also have one that is Walmart as the first name and Pharmacy as the last name.
3) Make sure you create the entry from the map application, or you add the address by using the map application, that seems to add some missing spice to the process as it is now, perhaps it adds the geo-coordinates, pehaps it just likes the little map icon in the photo space, I don't know, don't care either, I just know that adding the address from the map app helps. Here's how to do it in a nutshell: Find the place in the map app, tap the red pin, tap the blue arrow you will see on the marker that pops up, choose create a contact or add to existing contact whichever is apporpriate.
4) In SIRI, create your reminder and when it asks when you would like to be reminded, tell it, "When I arrive at (or get to or leave from or go to, etc.) Walmart Pharmacy." Substitute whatever first and last name you had created, of course. This seems to work for me most of the time, perhaps 4 out of 5 times. SIRI is in beta, after all, 4 out of 5 is not bad for beta.
Message was edited by: ACA