Folks might accuse you of NIH, but the quality of outside libraries is variable, suitable for a prototype but for shipping code you need control of ALL of it.
C++ Standard Library and Boost are of very high quality. It's quite tough to beat them.
On major platforms. But on embedded etc its hard to use any library - there are unintended dependencies.
{ embedded programmer }
Sure. You definitely have a point, but in context of the discussion here (ie Maro's code), I see no evidence that he is programming for an embedded system.
Things like move semantics and r-value references in C++1x will make them much tougher to beat. And for the most part they're not particularly hard to understand either. The standard library in particular, despite being a generalized library, is highly customizable and can be optimized for special cases (e.g. with custom character traits or allocators). Because it's a standard, good C++ developers should be able to use it. But if everyone reinvents the wheel developers would have to learn a new container or string interface every time they change jobs.
Plus they're open-source, so they're theoretically "yours" in the sense that you can compile and deploy your own. If you find a bug in Boost, you can fix it. We frequently deploy open-source libraries we've patched ourselves -- never Boost that I know of, but at least we know it wouldn't be a problem.
Similarly, you can extend them (or at least make your own code compatible).
Also don't forget licensing issues. It becomes important when you make a living of selling software.