Mash Creative, the author of the following designs,  is an independent design studio based in East London/Essex. They work on creative projects that include identity & branding, print media and web design. When designing logos Mash Creative always try to adhere to a particular set of rules :

Rule 1: Less is more – some of the most recognisable brands in the world use a simple marque or logo type – for example, think how simple the Nike tick/swoosh is.

Rule 2: If in doubt – simplify! (see rule 1). Strip away anything that may make the logo look fussy or overly complicated.

Rule 3: For Mash Creative a good logo should remain timeless. It is all too easy to design to a trend but a logo should have longevity.

Rule 4: Scalability – consider how the logo will look large and small. It is important that it remains legible, even when scaled down small – on a website for example.

Rule 5: If it works in black, it should work in any colour.

Excellent rules of thumb. Think of Apple logo as canonical example.

Why is it that a majority of the following (and most tech groups) either aren't using or don't have a nice logo, instead of a logotype?  Is it because the name = domain address and the emphasis/priority of the Brand is on the service/product, and not the aesthetic/abstract brand mark?  (It was probably so people could identify the companies using their own branding)via the recent OpenCo.SF 2013: http://sf.openco.us/Our group is the snake.  Oddly enough, we just started omitting the logotype/lettering.

Actually, yes. Logo is reinforcement of / advertisement for website.

Because until your brand is recognized that's really important.

Twitter may one day be able to use just the bird. But not yet.