There are a number of genetic disorders involving having an incorrect number of sex chromosomes. The general name for having the wrong number of chromosomes is "aneuploidy", and it can happen with the sex chromosomes too.
Turner Syndrome involves having a single X but no Y ("XO" ie - the sperm was lacking an X or Y chromosome). It is also known as monosomy X, and produces a number of symptoms, including shortness, the absence of a menstrual cycle, and infertility. Sufferers are still anatomically female, as the lack of a Y chromosome means there is no signal for the embryo to become male (all human embryos start out as female).
Triple X syndrome occurs when females have three X chromosomes, and actually causes limited symtoms (because of X inactivation "turning off" two of the X chromosomes in each cell).
Klinefelter's syndrome is XXY. The sufferers are anatomically male (due to the presence of the Y chromosome), but will be sterile, and are more likely to have some "female-like" characteristics (such as gynecomastia, or swelling of the breasts).
XYY men may have learning difficulties, but are often otherwise normal. They are *not* more prone to violence, and do not have elevated testosterone levels.
Other disorders, like XXXX, or XXYY also occur. As do unrelated disorders like Androgen insensitivity syndrome, where the embryo is XY (genetically male), but lacks the ability to respond to the developmental signals to become male, and so will anatomically be an infertile female. Interestingly, this disorder is an X-linked recessive trait (so a "son" will have inherited it from his mother, who was a carrier).
YY (or YO) is not possible, as there are several crucial genes that are found on the X chromosome, while the Y chromosome is relatively devoid of required genes (otherwise females wouldn't survive as XX). So any egg that lacked an X chromosome, and was fertilised by a "normal" Y sperm, or a "disomy Y" (YY) sperm would not develop, and would instead spontaneously abort.
Bear in mind that roughly 25% of *all* potential pregnancies are spontaneously aborted (often without the woman knowing she was even pregnant). The incidence increases with the age of the fertilising male - suggesting that errors in the sperm are a definite factor. The incidence also increases with the age of the woman, but this could also be due to a decrease in the function of the uterus.