Seems like a good place to start.  It's a question I get a lot.  "I want to play my amp at a lower volume, but get the same tone.  How about an attenuator?"  OK.  Let's start with what an attenuator does.  Simply, it goes between your amp and your cabinet, allowing you to turn your amp up to get all the preamp and power amp tone or distortion out of it, then lower the volume before it gets to your cab.  Some people prefer it because it let's you get that power tube gain but running the amp really hot, then simply stepping down the volume.  

So the question is, will your tone be the same?  Simple answer:  No.  Why not?  Well, it does "preserve" the tone of your amp.  But your guitar sound is a combination of a lot of things, and a HUGE part of that tone is your cabinets and speakers.  For a lesson on the importance of your cab and speakers, check out the videos page and watch the episode entitled "A Dissertation on Cabinets and Speakers."  But when you use an attenuator, you aren't driving the speakers as hard, so you move less air and as well, the breakup of your speakers (or at least their tone that's created from physically driving the cone).  So while it's better than simply using the master volume on your amp if you're trying to preserve your tone, it will never be the same - just closer than turning the volume down.  

Now, if you're going to use one one, get a good one.   Because of what an attenuator does, it is necessarily impacting the load your amp is seeing (or needing to see) from the cabinet.  So the attenuator also has to supply the correct load or you can fry your amp.  Make sure, therefore, that you get one that is rated at the correct impedance for your rig.  As well, make sure that the attenuator you purchase can also handle your amp.  I have literally seen attenuators smoke output transformers because the attenuator wasn't rated to handle the plate current rating of the amp.  Remember, when an attenuator creates the load for your amp, it's literally doing that through the equivalent of a big resistor.  If that resistor can't handle the load you're putting on it, it can cause it to fail, thereby leaving your amp without a proper load. 

Side note, one place attenuators can be very useful is home recording.  If you can't turn up at home, the proper attenuator can help a lot. . .