1) Lots of algorithms are built into tools. For instance, a relational database will generate an algorithm for doing the query by composing various parts. Some vague knowledge about the algorithms can help you write better queries, but you can do a lot of "searching" and "sorting", and when you use prebuilt libraries you can get code where people have thought about cache locality and all the practical issues of performance as well as the O() limit.
2) Knuth is obsolete. Learning CS from AoCP is like learning physics by reading Newton.