I use it along with many others. You are not forced to use the Strict DTD. You are not forced to validate. You've chosen to at least validate Transitional which is a step in the right direction. If you feel that opening a new window for links is something your visitors are comfortable with, then go for it.
Unfortunately the research and statistics show that spawning a new window from a link is as stated above by DrDoc and the others. I stopped using the target attribute a couple of years ago. Unfortunately, I do have projects that require the use of target for framesets and iframes and in those instances we at least validate Transitional knowing the only errors are those target attributes.
It is a little frustrating at first trying to work around it but, after a while it grows on you. There is a reason that target="" is deprecated, I'm still trying to justify it to myself. ;)