Reddit mentions of Photoshop CS4 Down & Dirty Tricks

You're off to a good start! Photoshop's a lot of fun, and honestly you'll never stop learning cool new techniques/tricks. If you're interested in quickly stepping up your game, I'd suggest giving Scott Kelby's book (one of his many, many Photoshop books) Photoshop Down & Dirty Tricks a read.

It's not a complete "how to do everything" or even a how to do most things book... but what it WILL teach you are the nuts and bolts steps required to pull off a lot of professional Photoshop techniques. It'll also give you a decent working grasp of a lot of the tools that Photoshop has. Basically, this book will allow you to skip ahead in your Photoshop learning/skills past the dreaded plugin phase (a great many Photoshop users at one time or another go through a phase where they use plugins to accomplish things they could better accomplish using Photoshop's own toolkit, and with a finer degree of control to boot).