Pullups DS18S20 and DS1307

I am using a DS18S20 and DS1307 in a project and everything seems to be working well. However I have a question about the pull-up(s) that is required on these items. Currently have I weak pullups enabled on the PIC and things seem to be functioning normally.

Should I be using external pullups or are the internals OK? The reason I ask is because I see the pullup is disabled when a pin is an output. In both cases there are times when the pins requiring a pullup would be outputs, thus they would be missing.

Thoughts.

With regard to I2C, external pull-up is really mandatory on the SCL & SDA lines. 4K7 would probably suffice for up to 5 devices on the bus.