I think the main problem you are having is that last line being longer is affecting the alignment of the lines above it. So, you can use mathrlap so that the last line's length does not affect the alignment:

Note that the = is right aligned to the alignment point specified. This is because the usual alignment is: stuff to the left of an equal sign is right aligned, and stuff to the right of the equal is left aligned.
However, if you want the last text to be left aligned then I would recommend using an alignedat instead:

Code: aligned
\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{align}
\begin{aligned}
\text{some stuff} \bigg\{ & \text{stuff }' \\
& + \text{stuff }'' \bigg\} \\
=\mathrlap{\text{some other stuff}}
\end{aligned}
\end{align}
\end{document}
Code: alignedat
\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{align}
\begin{alignedat}{3}
&\text{some stuff} \bigg\{ && \text{stuff }' \\
& && + \text{stuff }'' \bigg\} \\
&=\mathrlap{\text{some other stuff}}
\end{alignedat}
\end{align}
\end{document}
\left...\rightconstruction over a linebreak. So where exactly is Herbert doing it wrong? To me it looks more like you want to place an additionalalignedinside the\{...\}. Note in that case that the\{goes before thealigned, aligned should have an additional[t]option, and the\}goes inside the aligned. – daleif May 07 '14 at 17:04some other stuffto be aligned on the left in which case a\mathclapvariant may be needed. – Peter Grill May 07 '14 at 17:15\MoveEqLeftwith a&and you get the ascii drawing, I just prefer this version. – daleif May 07 '14 at 17:20