Yohimbine is usually considered an agent that helps to reduce body fat, increase sexual desire and ability for men as well as a stimulant that may cause unpleasant adverse effect of anxiety together with elevation of blood pressure.
However, according to the literature, yohimbine has some other effects as well, including effects on cognition, memory and sleep that may be of interest. Yohimbine (30 mg) reduced errors on letter flank test . A simple version of letter flank test that shows ability to filter out irrelevant stimuli from detecting target letter is available online . However, it increases rapid response impulsivity and errors in a somewhat more complex immediate memory test that has numbers instead of a single letter; the used dosage was a comparable 30 mg dose for a 75 kg person. The problem that occurred with yohimbine was that the test subjects did not read the number thoroughly and prematurely thought that the number was similar to another number presented just before the current. The test is explained online  but is not freely available.
Interestingly, yohimbine seems to have a truly interesting sex-specific effects on both memory and cognition of fear. Without affecting learning, it interrupted ability of women to generalize from learned memories . Furthermore, the effect of yohimbine for processing fear-related signals (alteration of amygdala activity) is opposite for men and women .
A small study with medical students as subjects used a low dose. It was found that yohimbine improved following cognitive abilities: reaction time (single choice, not multiple choice), critical flicker fusion threshold and working memory (as measured by 1-back and 2-back tests) . However, during glucocorticoid treatment or during high stress, yohimbine may be counterproductive for higher, flexible thought: yohimbine and cortisol together may reduce goal-directed behavior in favor of habitual behavior .