The Deepholm Herbalism path is a function of the geography of the zone more than anything else.
There are two small concentrations of herbs in the yellow circled areas on the map. Beyond that, the herbs in the zone -- Heartblossom (which is unique to Deepholm) and Cinderbloom -- occur relatively dispersed throughout the zone in any area that has flat surface. The only area that possesses fewer nodes is the lowest central area, and should usually be avoided in your flight route.
Deepholm has three tiers, a low tier, middle tier, and highest tier. Given the extreme elevation change between the tiers, it makes sense to fly in a circular pattern around the zone as represented by the blue line in the diagram, weaving at the same relative height so as to avoid major elevation changes while farming.
Depending on how the Cataclysm expansion economy shakes out, Deepholm may be a very profitable zone for herbalism because of its unique herb: Heartblossom. As it probably isn't the "best" zone for either Herbalism farming or Mining farming, it may become an under-used and therefore not-as-contested zone. Part of finding the optimal spot to farm is not just finding the materials that sell for the most gold on the auction house. The other important factor is how many of those raw materials can you acquire in a given period of time. Deepholm has the potential, especially if you have mining as your other profession, to be a forgotten zone for finding a lot of non-farmed nodes ready to be gathered.
Mount Hyjal Mining Route
Vashj'ir Mining Route
Deepholm Mining Route
Uldum Mining Route
Twilight Highlands Mining Route
Mount Hyjal Herbalism Route
Vashj'ir Azshara's Veil and Stormvine Route
Deepholm Heartblossom Route
Uldum Whiptail Route
Twilight Highlands Twilight Jasmine Route
Tol Barad Azshara's Veil and Whiptail Herbalism Route