Good Morning, Marketing Chick-and welcome to the forum. I've personally found this place to be nothing short of a wealth of knowledge, as I'm sure you'll find the same.
The other person had touched on a very good point--If you're not doing this on a regular basis, you should be because you very well could be losing a potential nice slice of pie.
If we don't get a bid, and it's in fact a project that we WANT,....I personally give it a good couple days until after our bid,...Call the customer, first and foremost start the conversation by "Hello, Mr./ Mrs.__________. This is _________ w/_____________(company)--We're in fact the ____________company that had the pleasure of visiting with you a while back (or be more specific) in regards to the ____________project that you folks were planning on doing/ pursuing. I simply wanted to "touch-base" out of courtesy to see where things stand.
****Keep in mind, it's always nice to have some sort of "call to action" (depending on what type of product you have, you may in fact want to see if there's any tax credits available that they may take advantage of that weren't available at the time of your initial estimate if indeed you're going back a couple years---Just a thought)
If you recall any specific details of the visit, maybe bring something up that you may have discussed just to make the call a little more personal as opposed to a straight forward reach to their wallet....lol
All in all, what you're attempting to do is a definite way of generating business, and IMMEDIATE business, and it's a great idea if done correctly.
--You can also do this with your existing customer base, as that also can be a great resource for generating an immediate impact--maybe offer a 10-20% discount for previous customers, etc.
Hope this helps!--(But what the hell do I know...:w00t