For the price, you won't find a better overdrive. Pros: well-built, sturdy, and a fairly neutral overdrive that won't color your amp's tone (some say it adds a bit of high end, but I haven't found that to be the case so long as I work the tone control). Cons: not a lot of volume on tap and a touch noisy (all OD pedals are noisy to a degree).
If you're running the SD-1 in front of a clean amp and are using single coils, you'll get more than enough of a volume jump when you step on the pedal. But if you run the SD-1 in front of a mildly overdriven amp and are using humbuckers, you'll have to crank the level knob all the way just to get a tiny boost.
I have two other overdrives (Electro-Harmonix Soul Food and MXR M-66 Classic Overdrive), and the SD-1 compares favorably to both. It doesn't have nearly as much attitude or volume boost as the Soul Food, which provides a much tighter, more focused overdrive (think of a cranked Marshall JCM800), but again, the SD-1 is more likely to stay true to your amp's tone. Although I like the MXR slightly better (it falls somewhere between the SD-1 and the Soul Food), it's on the fritz (it died unexpectedly), so, assuming the SD-1 holds up like every other Boss pedal I've ever owned, that's a plus in its favor. For now, I'm using the SD-1 and the Soul Food on my board: one for neutral overdrive (SD-1) and one for extra sauce (Soul Food).
All in all, a great value.