How loud should a singer sing?

How loud should a singer sing?
In popular music, it is often thought that 'louder is better'. This is not always so. Often, increasing the volume makes the subjective effect less, not more.
Source: www.record-producer.com

Young Jeezy, Kanye West & Jamie Foxx Lead 2006 Billboard R&B/Hip-Hop Awards
Young Jeezy now has more reason to proclaim "yeeeeaaaah..." While the ATL-ien nabbed 4 nominations for the 2006 Billboard Music Awards behind Kanye West (7 nominations). The highlight of this...
Source: rap.about.com

Is your sound so distinctive you could have your own plug-in? (It's not a good thing!)
Some bands and artists have a sound so distinctive that you could almost have a plug-in for it. But is this a sign of artistic limitation?
Source: www.record-producer.com

Three microphones tested on female vocal - should a better preamp have been used?
The recent test of three microphones on female vocal used a Focusrite Octopre preamplifier. Was this a good choice? Should a different preamp have been used?
Source: www.record-producer.com