Making it too large would lead to slow rise times, and, in extreme
cases, even noise pickup.
1k was popular for early TTL but is unnecessarily low for many modern,
low-power CMOS applications. 100k strikes me as being on the high side
for most (not all) applications. 4k7 or 10k is often about right for
One thing to watch out for is when the pullup is on a bus (such as I2C
/ SMBus). The devices used for this have a section devoted to
calculating the pullup resistance required (it's dependent on the
number of devices attached, but that's always true).
For pulling up a single pin, I agree on the 4k7 / 10k rule. If you have
to pullup / down a tri-stateable bus, then bus speed becomes a major
issue. Slow busses can be pulled with 100k or so, but fast ones ( <
25MHz or so) need more of the order of 4k7.
If they are faster than that, you may need to look at proper