A source of extensive information on astragalus, and astragalus formulations, including a list of over 300 clinical studies, is at vidainstitute.org . I have summaries of many of the studies which I can provide if anyone is interested in any particular one. The site also has an interesting page on another herb called Centella Asiatica or Gotu Kola. The site is not complete yet, and more will be added in the coming days.
I personally have been using a regimen of large doses of raw astragalus root (30g+ per day), tea made from the root, and extracts, some with the addition of Centella Asiata, for several weeks now, and have gotten results that are nothing short of amazing. A fairly serious back problem (compressed disk, osteoarthritic degeneration) is greatly improved, as well as osteoarthritis in a shoulder, and another condition called Laryngoesophageal Reflux Disorder (LERD) seems almost entirely cured. I am physically stronger and more energetic, and my memory is improved. It even shrank my hemmorhoids! After adding Centella Asiatica to the regimen, I even have gotten effects on my eyesight. I can read a paperback novel now in good light - something I haven't been able to do in years!