Am I allowed to write about a discovery, while pending acceptance of my manuscript on the same topic?
This depends on the field and/or the journal. My understanding is glam-mags (Science, Nature) do indeed tend to prohibit any mentioning of the paper contents. On the other hand, for say mathematics journals it would be common to have a preprint on the arXiv anyway, so for something of particular interest, a lot of coverage can arise prior to the actual publication (see the proof of Kepler's conjecture for an extreme example).