Switching to new running shoes: all at once, or work between "old style" and "new" shoes?

Every time I switch shoes (even new ones from the same model) I gradually adapt to them. 

Bummer on the Hurricanes...they didn't work for me but I know they're great shoes.  Glycerins are also good (I run in the Adrenaline) and I don't thing they're going anywhere.

I don't go crazy on shoes like some people do.  I have seen people make post on which of their 6 pairs of light-weight trainers they prefer for tempo runs on the road and which they prefer for intervals on the track.  They also have 6 pair of stability shoes and post which they prefer for long runs and which they prefer for recovery runs.  They have 6 pair of race shoes with preferences based on race type and distance.  They have 6 pair of shoes just for fun to experiment around with.  The first decade of my running career I just had one pair of running shoes that often doubled as my every day shoes too.  When they were replaced I though the old pair out and only wore the new pair after that.  When I was in college my coach told me that it you could find two brand of shoes that fit you well that it would be worth it so that you could rotate shoes every day.  He said that would work your legs a little different between the two pair which would improve the training benefits.  i also noted that it would allow shoes to fully dry out between uses that would extend the life of the shoes.  So...I now try to keep two pairs of train shoes in the closet all the time.  I only use them for training until the cushioning is all worn out (as I can tell by how my knees feel after a run).  After I retire a pair of shoes from training they become my every day shoes.  I am always rotating shoes so when I get a new pair I a m not wearing them for every run.  Just every other run.  :-)  Note:  I did the new out of the box challenge at a half marathon two years ago.  I brought a pair of shoes with me on race day that I had never run in before.  After my warm up I put them on and raced in them.  No blisters, no issues, and I PR'd by 3 minutes.  I think lots of the Pro's race in new shoes right out of the box them discharge the shoes after the race.  Like I, I think they have had the same model they race in to run in previously so they know that the shoe is compatible with their feet and running style.  I got a pair a shoes once that were not compatible with my feet. Running style and I got shin splints.  So, there is some risk go into a new pair of shoes but if you are smart about it and make adjustments if needed you should be able to pick up a pair of shoes and run in them without needing a break in period.