Sometimes the best offense is a good defense. This applies to the world of hormones at times as well. For example, the most obvious way to solve low testosterone, or hypogonadism, is to add testosterone, right? Well, there's another way: add a SERM such as Clomid (clomiphene citrate) instead.
What is a SERM? It means that it will in some tissues act as an estrogen and in others block estrogen. However, the bottom line is that in males it generally works its hormonal magic by blocking or inhibiting estrogen at the hypothalamus which, in turn, stimulates GnRH and, further downstream, LH (leutinizing hormone) in the pituitary. Males can see their low testosterone levels double or more, especially in the case of secondary hypogonadism.
Some decent research and years of clinical practice have born this out. For example, one study put 36 men with average total testosterone of 248 ng/dl on 25 mg/day of Clomid and after 4-6 weeks the men's average testosterone was a much improved 610 ng/dl.  This is a nice boost indeed, especially for what is considered a relatively low dose of Clomid. The authors also point out that the all-important testosterone to estrogen ratio was raised from 8.7 to 14.2.
We have had a couple of Peak Testosterone Forum member who were enthusiastic Clomid users. Look at what this guy wrote:
"Yep, seems like I 'passed' the Clomid challenge. February I had a reading of total T at 270 ng/dl. Today's results, after 5 1/2 weeks on Clomid: 627 ng/dl!! Wow, so that was really good news..." 
Clomid also has certain advantages over standard testosterone therapy. HRT requires shots or topicals that require time and potential risks. It's nice just to take a simple pill, as is the case with Clomid. And the good news is that Clomid seems to generally raise testosterone in the younger men who try it, which is still more evidence that the great majority of men have secondary hypogonadism. Also, it is worth pointing out that a significant percentage of men have what I would call an "HRT-like" experience from Clomid, i.e. it improves libido and erectile strength and they feel better as well.
However, many have th opposite experience where their testosterone increases but they get no increase in libido. We have had men shoot up into the 800's or higher on Clomid and yet have absolutely no increase in sexual desire. This shows just how Clomid can negatively impact the male brain due to its sometimes estrogenic qualities. And there is simply no way to know if you will be one of the lucky or unlucky ones.
So how safe is this convenient Clomid? In the short term, Clomid seems quite safe it can have side effects such as visual disturbances and headaches that should be discussed with your doctor - and that is one reason that some doctors are increasingly prescribing it for hypogonadism. Clomid has been taken for years by males as a fertility treatment due to its testes-stimulating powers. So it has a reasonable track record considering that it has been out for awhile.
One other crowd that has used Clomid for an extended period of time are steroid users and certain athletes. Steroid men will use Clomid to get their testosterone back, a common issue with steroid abuse. It is commonly used upon completion of a steroid cycle to "jump start" testosterone. Often testosterone will collapse after steroid use and Clomid is the only thing that will bring back testosterone and estrogen within normal physiological ranges. This was documented when one study discussed Clomid's effective use to do just this with a "steroid abuser". 
The bottom line is that Clomid has been used extensively by many men off label and even non-legal users and all have found it to be reasonably well-tolerated with low side effects for short term use as long as low doses are used and certain procedures are followed. I discuss some of the side effects below, and, of course, you should talk to your doctor first before going on Clomid and discuss risks/rewards. NOTE: Clomid does not always work. If you are primary hypogonadal, for example, Clomid will do nothing for you. And the same is true if you have pituitary damage..
CAUTION: Many men now want to use Clomid long term. Talk to your doctor, but I think this is unwise for a variety of reasons that I go into detail about in my link on Your Risks with Long Term Clomid Usage. Below I give a quick summary, though, of the issues involved:
1) Vision. A surprisingly common side effect of Clomid is blurred vision and some would add floaters. However, one important point is that this risk is greatly reduced with low dose Clomid. By low dose, I mean 12.5 mg MWF or maybe 25 mg MWF at the most. Now you have to talk to your doctor about risks, but the general advice that I have seen is that one must quit Clomid and call your doctor's office immediately if you experience any visual disturbances.
2) Moodiness and Estrogen. Clomid is actually estrogenic in some cases and moodiness and mood swings are fairly commonly reported. The bottom line is that Clomid's effects are poorly understood and likely vary from individual to individual.
3) No Increase In Libido. Many men will see their testosterone double or even triple on Clomid. With that kind of increase in testosterone, you would expect a nice boost in libido. However, this often does not happen, and the reason is that the estrogenic effects of Clomid probably outweight the increase in testosterone in these men. Unfortunately, you just don't know if you're one of the lucky ones until you try.
4) Thyroid. Some of Clomid's common side effects match up quite well with those encountered during various thyroid issues. This has some wondering if Clomid does subtely affect thyroid function in some way.
5) Nausea or Headache. These are fairly common side effects with Clomid. Again, your doctor should be called immediately if this is an issue.
6) Clomid. Clomid raises SHBG enough to where it could be an issue for some men with high SHBG. As SHBG rises, the percentage of free testosterone can fall. Ideally, you want this range to be 1.5-2.5 percent of total testosterone. See this link on High SHBG for more information.
1) J Sex Med, 2005 Sep, 2(5):716-21, "Clomiphene citrate effects on testosterone/estrogen ratio in male hypogonadism"
2) Fertility and Sterility, Jan 2003, 79(1):203-205, "Use of clomiphene citrate to reverse premature andropause secondary to steroid abuse"