I used to follow up after all quotes but found that I would typically get the job
within a week or so of quoting them and the ones that were follow ups,
generally were tyre kicking. I dont often follow up anymore.... 

We usually wait a good year or so as we have found that very rarely customers
will randomly call up and say that they'd like to go ahead with a job you
quoted 8 months ago. We do however, move jobs that have passed a 1-2 month
window into a area which is classified as jobs/quotes that are 99% dead,
but you never know.

Brian, - Good question - may I suggest the old adage - he/she who "waits" is lost!
I learnt many years ago IF the quote is qualified and I am going to submit
the quote then it is MY responsibility follow it up. i.e. only quote
project we really want in the first place. With that being the case we
would only submit say 50% of the projects we had been offered preferring to
refer projects not in our best interest to friends who suited their type of
work. Then responding typically in an appropriate to time frame depending
on circumstances, size of quote or the like. Therefore in some cases in 24
- 48 hours I would call and just ask " Hey I sent though the quote, are 
there any areas needing clarification or explanation. We know quotes are
often open to differing views and methodologies and we like to ensure our
clients have all the facts they need." Funny thing is more often that not
the reply would be, we don't have any others submitted their quotes yet. A
chat develops which can often build trust and YES, typically the client
would give you the order - like they say " the early bird gets the worm"
and importantly increasing the ratio of projects we really want while
passing on those we don't. If you have ever heard my "FHT" seminar it is
really all about doing the work you choose from the customers you best
profile to suit your business.
(John, Controlzone)

Sometimes we get immediate notice and some customer can take up to 3 month
- on all our quotes its stated that the price is only valid for 30 days -

Basic Signs (ie. 900x600mm flat or decals on 2 car doors) quote during enquiry or
within an hour. Fabricated with neon/LED, top-of-building, crane install,
with possible engineering requirements 2-3 weeks, but the client is
informed (and usually expects) it to take time to work out.

6 hours 

Depending on the complexity of the project, from a few hours to a few days.
However, I will call for up to three quotes for a large project but may
proceed early if an acceptable price has been reached with a prompt
supplier. Sometimes I think the willingness to provide a prompt quote
translates to a production team that is interested getting the job done
quickly too.
(Michael, Test Lab Software)