Corrected entry: Season 5, Episode "Sex, Losers and Videotape." Grace is trying her darndest to make a sexy video to send to Leo - why? He's working on a viral outbreak in sub-saharan Africa, and he told Grace in an earlier episode "these people don't have running water." Doesn't make sense that his precious cargo of food and medicine would include a VCR, even if electricity is on hand.
Corrected entry: Season 5, Episode "Bacon and Eggs." After multiple rejections, Grace finally decides to call Leo. She pulls his business card out of her wallet, presumably to look up his number, but barely glances at the card as she dials. (This would be plausible if she memorized his number, but if so, why pull the card out?)