I know 3 people (personally, in real life, as more than casual acquaintances) who utilize exogenous testosterone. Only one of them does it legally, and under the supervision of an experienced GP and endocrinologist.
He was frustrated with general fatigue levels, an inability to sleep, and completely stalled progress on his powerlifting. He finally went to his GP, and they tested him, and he was low. After trying the androgel and disliking it, he now takes a weekly injection that puts him at the mid-to-high levels of physiological "normal".
He was astounded by the results. More energy, more "zest", better lifting, better mood...he suspects it might have helped smooth his marriage out a bit. He's 41 years old, and his family and friends were glad to see the "old" him back.
The potential for abuse is there, but it's a legitimate medical practice that will see a more widespread acceptance in the next decade or so, as someone mentioned above.
Not for everybody, but nothing to be ashamed of doing, if necessary.