Refactoring our documentation a bit for M10 will help, the predictive interface in M9 helps, and there are some cool "code hint" ideas that are coming in M10 that will hopefully make it easier to keep learning.

We'll also soon be launching a community site to make it easy to discuss functionality, seek answers, and share code. For now, http://mathematica.stackexchange.com is a good resource.

We're also working on getting some materials about the Wolfram Language that should make it easier for people with existing programming experience to grok what is unique and different about WL, and how they might go about learning it.

Probably the best resource remains the existing Mathematica documentation. It is vast -- containing for example more than 100,000 evaluatable code snippets that demonstrate each function being used in multiple ways.

It is available online (http://reference.wolfram.com/mathematica/guide/Mathematica.h...) as well as in-product (double-click function you want to know about, then press F1 or Cmd+Shift+F). Following hyperlinks from familiar territory can get you a long way.

It's quite easy to get lost in it, of course, so here's a short list of "bread and butter" functions that I think every WL programmer should know really well: https://gist.github.com/taliesinb/5848321

Lastly, here is an eclectic mix of guides that might serve as good 'anchors' for some documentation spelunking:

http://reference.wolfram.com/mathematica/guide/LanguageOverv...

http://reference.wolfram.com/mathematica/guide/RulesAndPatte...

http://reference.wolfram.com/mathematica/guide/Patterns.html

http://reference.wolfram.com/mathematica/guide/StringPattern...

http://reference.wolfram.com/mathematica/tutorial/BlocksAndL...

http://reference.wolfram.com/mathematica/tutorial/LevelsInEx...

http://reference.wolfram.com/mathematica/tutorial/ApplyingFu...

http://reference.wolfram.com/mathematica/tutorial/Manipulati...

http://reference.wolfram.com/mathematica/tutorial/Introducti...

http://reference.wolfram.com/mathematica/guide/SymbolicGraph...

http://reference.wolfram.com/mathematica/Compile/tutorial/Ov...

http://reference.wolfram.com/mathematica/guide/GraphsAndNetw...

http://reference.wolfram.com/mathematica/guide/MatricesAndLi...