Longtime Rock Band veterans won't be too impressed by this, but let me just say that I am very prooud of my recent unlocking of the "Solid Gold, Baby" achievement in Rock Band 2. The achievement is unlocked by earning a gold-star rating on a song. Unlike in the Guitar Hero franchise, however, you can't get a gold-star rating by simply getting 100% note completion on any song in any mode (normally, Easy). RB2 only gives out a gold-star rating if you play on Expert mode and earn a score roughly equal to 1.5x the score necessary to trigger a 5-star rating. In short, this requires near-perfect play. You have to not only hit almost every note (certainly can't drop a combo), but you have to also know precisely when to use the Overdrive multipliers to chain them together.
I earned my gold-star rating on "I Think I'm Paranoid" by Garbage, playing Bass on Expert mode. I finished with a 414 combo (entire song) and got the Gold-Stars to trigger on my 4th to last note in the song. That's probably the easiest song to get this achievement on, especially on bass, But it still took my about 6 or 7 tries, not to mention a lot of time spent playing other, harder songs to get my skills up.
I was so excited about my combo, score, and the gold stars that when the song was over I ran up the stairs to get my camera to take a photo of the tv for this inevitable blog post. Unfortunately, I bumped the guitar as I ran up the stairs and advanced past the score screen.
Stupid wireless controllers.