If someone on the street tells you their web site is "mister smith dot com"...
 

would you type

mrsmith.com or mistersmith.com?

and the same for

drsmith.com or doctorsmith.com?

i have a site doctortushy.com but some type drtushy.com

mrsmith

Just register both.

One of my domains has the word "gray" in it, I registered the same with "grey" as well, and forward it.

mrsmith.com

mr is what i would think, but knowing me i would ask :)

mr

mrsmyth.com
mrsmythe.com
mrsmthe.com

I'd buy all the variations I could think of if I was going to buy a type-in domain. People can't spell.

I own all of the above.