But he didn't do that well against the austrians, did he? Despite his tactical skills (taking advantage of a fast-moving army?) he just managed to barely hang on to Silesia - against mostly inept austrian generals.
For the entire war of the Austrian Succession, he had remarkable success; for the first third or so of the Seven Years' War, he had similar battlefield victories. He did barely manage to hang onto Silesia, but he conquered Saxony in the first months of the war and hung onto it for the entire time, relinquishing it at the end of hostilities. The revenues that he drew from there proved critical in his ability to continue the contest. Throughout the rest of the war, he'd continue to score the odd success, but remember that tiny Prussia was attempting to maintain itself against Russia, Sweden, France and Austria. It's pretty amazing that he kept them all from killing him.
As for the skill of the opposing generals, Daun was good, but he was no Friedrich. By the Seven Years' War, Austria had competent professionals in service - remember, when Friedrich decided to drop out of the Austrian Succession war, the Austrian marshals were skilled enough to push France all the way back to Alsace before Prussia jumped in again - but against a general of Friedrich's caliber, good wasn't really good enough.
Friedrich's tactical skill was mostly geometric, not movement-based, and also had to do with his army's ability, via intense drilling, to carry out tremendous feats of arms (like the great wheel at Sohr, for example).
innonimatu said:
He was lucky that neither Austria nor Russia pressed on with their wars with Prussia, and that the french never really committed to it.
Oh, Austria pressed on it all right; they had little else to do in the Seven Years' War anyway. Fred was just that good.

Aaaand he had the aid of a Russian expeditionary corps for the last few months of the war. That helped a bit. But Russia dropping out when Elizaveta died was a tremendous stroke of luck, yes. As for the French, well, the fact that they lost the Battle of Minden against Friedrich's western army of Brits and Prussians led by Ferdinand, Herzog von Braunschweig was rather important in their relatively low contribution thereafter; French troops did take part in the Battle of Rossbach (where they got
royally creamed

), but never after that really threatened Friedrich's main position in Brandenburg proper, Saxony, and Silesia.