I've never really liked baby talk, and pretty much find myself unable to do it despite it likely being useful. Possibly in consequence DD was certainly not early in her speech (under 50 words at age 2) however by age 3 her vocabulary and speech was excellent, so I don't feel long term it was a bad thing - not that I could've really gone against my nature anyway.
DD is now 3.5, her speech is very good, but some people who talk a lot with her -especially MIL- are still using real baby talk around her, using a smaller vocabulary than DD and exaggerated pronunciation with her. Not that it actually matters as far as I can see, but it's got me wondering when baby talk actually stops for most people?