First, do BDunn7, it would help to know exactly what you did. The only thing I can think of is you set up Desktop Manager to sync with your Yahoo account.
To Green Cart, I don't use google, so don't know except what I read here. I gather adding the google app creates issues for some that they have to correct, but simply adding an email address to BIS does not create the sort of problem the OP seems to be having and for which you seem to be issuing a warning. I've used Yahoo on BIS for certain purposes with no problem.
You are very loose with your advice. What is BB email? Are you talking about the BIS, about the carrier-provided blackberry email address, what?
FYI, there are numerous reasons to not rely solely on the carrier-provided email address and to be very select in what you use it for. It isn't available when BIS goes down. You can only read it on the blackberry. Once the email is deleted from the blackberry -- i.e. you accidently delete it -- it is gone.
I don't know what you are talking about with Outlook. Too complicated? Or too complicated for you? Why not give a specific example?