The cartographers of the old times did not actually use this phrase as often as many think. This English form was not used in historical maps. According to experts, there is one map (a globe from ~1503) that has the phrase "HC SVNT DRACONES" ("hic sunt dracones", "here are dragons") placed in Asia.
Of course, cartographers did draw pictures of dragons and monsters to the maps, and included other phrases that described the various threats that were around in those areas: warnings of lions, serpents, and other monsters were often found.
There were maps that had "Hic sunt leones" ("Here are lions") in Africa. Later on, they used this phrase everywhere to describe any places with as of yet uncivilized "savages".
(I guess patriots and sports fans here in Finland will use the lion version of the phrase, considering the animal is found in national coat of arms and from the name of our ice hockey team)...
Of course, modern maps have used the phrase too. Michael Gaffey labelled the uncharted area of asteroid Vesta "terra incognita", with explanation "here there be dragons", in a paper submitted to science journal Icarus.
"Here Be Dragons!" is also the name of my all-time favorite web site about dragons, complete with amazing amount of stuff of dragon physiology...
- Carpe Diem: Hauskaa ja hyödyllistä Latinaa, Arto Kivimäki, Karisto 1998, ISBN 951-23-3661-8.