When it comes to echoing or setting do you prefer ' or "

[eluser]Sarre[/eluser]
[quote author="Craig Rodway" date="1201107424"]Single quotes for strings where I don't need variable access, and double-quoted for strings where I need to access variables (but only with curly braces - this is quicker than just placing variable references in strings).

Code:

$name = 'Craig';
echo "Hello world, my name is {$name}!";

[/quote]
Erm? Why exactly with curly braces? I never use those...
Is there a big speed difference?