It's less easy to quantify your progress than with weight lifting (whose easy conversion into numeric growth I wonder isn't one of its attractions when you're a data-driven kind of person) but has further reaching benefits beyond basic physical strength.
After 3 years of fairly regular yoga practise (3-4 sessions a week), even when combined with a fairly poor diet/lifestyle alongside it (way too much fun), left me feeling stronger, fitter, calmer, more centred, more energised* than I ever had before.
For those of you who, like me, are put off by the more 'hippy' aspects, I'd say it's a question of finding the right teacher rather than writing off the entire practice (my teacher at the time was nicknamed 'El Sargento' for her, shall we say 'strict' approach -- she taught Iyengar yoga with is a lot about details. This didn't suit everyone but suited me down to a tee).
There is an awful lot of pseudo religious bollocks that surrounds it but within that there's a really solid method for improving the quality of your life.