At 2.4 volts you can actually use LEDs without resistors. There isn't much opportunity for high currents to develope. Moreover, having resistors, you don't get enough brightness. But that's a special case. Also many ICs seem to have some kind of current limiting built in already.
There are nice SIP resistor networks, 4 resistors, one common ground. Futurlec has them.
It's OK for indication LEDs to share a resistor, however, this isn't professional (unless you use some tricks). You get brightness variation if more than one LED is turned on. Also I never really see it in circuits or on PCBs. If you only light one LED, it's the same as having 3 resistors. You could even multiplex 3 or more LEDs only for the purpose to save resistors (using software).
Using high efficiency LEDs for indication, it is not much sense to leave out the resistor- you get disturbing high brightness, and with some ICs, the LEDs will burn out.
What people normally do is:
-use resistor networks (SMD), however, can be hard to solder.
-use SIP or DIL resistor networks, some vendors have them at good prices.
-use smaller 1/8w resistors not much difference to 1206.
The 74hc164 actually has 120 Ohms built in (Texas Instruments datasheet).
It's still too much brightness for indication (can be disturbing), unless you switch off (reset) the serial register very quickly after loading data.
How many LEDs do you use on your PCB? And what they are used for, actually?
Removing components isn't lazy. Examine a common "old world" VCR, and you see PCBs actually having many empty spaces, originally intend for various components.
I see it repeating endless again and again mysterious lazy hobby tinker people using LEDs, and the same popping up in smoke, or burning out quickly.
I ask to people who write such replies: How many real world cases actually do exist, where people made PCBs without LED resistors, and they popped up? And what's the matter if you fry one 5 cents LED? How many people actually have done it again after they burned one LED?
I guess it's more kind of a rethoric reply, and such hobby tinker people are only (forum based) fiction.
I made some CPU bus panels, having 32 small LEDs altogether, plus 32 resistors. I wasn't interested in high brightness, only to see the binary signals resulting in LED lighting up. The resistors are required since a CPU bus does not have so much power. It's not really serious point of discussion to leave out the resistors here.
Can't we establish one simple single line forum rule here: "Fry LEDs at your own risk"? Or someone could create a web tutorial only about LEDs and resistors, and how to drive LEDs using various ICs/controllers. Seems to be a popular topic on many forums.