There is a tension in Lojban, as in natural & other constructed languages, between the need for brevity and the desire for accuracy. In addition, the whole concept of figurative language has an uneasy place in both Lojban theory and practice. Probably the hardliners who would limit metaphorical usage to those phrases marked by PE'A (or the cartouche FU'0PE'A...FU'O) are doomed to be defeated in the long run by the inherent fuzziness of human semantic space, but there is something LOBYKAI & even noble in the attempt to draw this distinction with rigor. In defense of the stricter view, there is quite a lot of latitude in wielding the GISMU themselves, so long as the thing referred to does indeed have the features indicated by the SUMTI-slots... But the amount of poetry in calling a GERKU a DANLU or a SE KERFA will not, after all, carry us very far.
First, there are those idioms which are more or less sanctioned by repeated usage:
SKUDJI 'express-desire' for "want to say", is common and almost orthodox. CISKYCUSKU 'writingly express', once frequent, seems to be losing out to FINTI 'invent'. NORYRU'I 'semi-spirit' for "ghost", and XA'UNRO'A 'dweller-prose' for "diary", are useful coinages that have not yet been approved by the community at large. LE JBOSTE 'Lojban-list' is, although clearly a calque of the worst sort, now the canonical name for the internet mailing list, which might more properly be made from MRILU, BENJI, or JUDRI. JI'ANAI for "except" is difficult to find a better alternative to, but not quite what the original meaning of JI'A 'also' would entail.
Then there are isolated suggestions, for which this place must be thought a kind of limbo pending the emergence of a body of fluent speakers who can dispense with both prescriptive and descriptive interference of this sort...
BESNA JE BETFU 'brain & belly' for something like "body & soul". FEBVI JOI ZALVI KO 'boil and grind you!' for a very serious pejorative.
Lojban is by now a living language, and the words in fashion are always changing. It's interestingly complicated by how much of our history remains; I'm reading what's written here and learning more about our language-- & thus again shaping its future path. Indeed I've never recently heard "ciskycusku," though "skudji" remains popular. One word that's been common lately is "ckakla", ckana zei klama, bed-go, to go to bed, which is well-liked as a pun with "cakla", chocolate. :) --mungojelly