I'd like to ask "What exactly is considered a lot of traffic for a website?"
What's the minimum someone could say - after stating their website receives a lot of traffic - as to not be laughed at?
Inspired by this question on stack overflow
I've created the following scale to help give some feel of what "a lot" might mean. It uses estimates of unique monthly visitors for popular websites to create a high point, then works down from there.
The "what's a lot of traffic?" scale (monthly uniques):
Examples below based on collected data points of varying accuracy and usefulness:
1 billion unique monthly visitors (a right royal load)
Google's estimated monthly unique visitor count is around a billion, as reported by the Wall Street Journal here in June 2011, based on comScore's estimates.
714 million unique monthly visitors (a mother load)
Facebook's monthly visitors are almost as high as Google's, according to the same comScore report that the Wall Street Journal cited.
400 million unique monthly visitors (a crap load)
The Wikimedia foundation reports around 400 million monthly uniques for all Wikimedia sites worldwide (e.g. Wikipedia).
46 million unique monthly visitors (a boat load)
A popular news site, such as the Guardian reports its monthly unique browser count at about 46 million. This is in line with other large news websites: The Huffington Post reported 36.6 million uniques and the The New York Times reported 35.5 million uniques, both from the US alone [source].
20 million unique monthly visitors (a boat load)
A popular Q&A family of sites, such as the StackExchange network, sees around 20 million uniques per month, according to union square ventures in March 2011.
8 million unique monthly vistors (a lot)
5 million unique monthly visitors (a lot)
More than 100,000 unique monthly visitors (quite a lot)
Popular and moderately famous blogs and sites live in this band. (Anecdotal data point: I used to run a small popular blog that got about this amount of traffic. It's a healthy amount of traffic to have. It's also about the number of monthly uniques you need to make AdSense/ad units worthwhile, in my opinion.)
Fewer than 100,000 unique monthly visitors (small fish)
Everything else—hobbyist blogs and websites—fall here.
"A lot" is a relative term, so it's important to note that the scale above is only a very loose guideline. Many webmasters would be perfectly happy with a few thousand uniques a month for a personal blog, for example, and may well deem that "a lot". It depends entirely on the context, the competition, and the extent to which your own sense of achievement is inflated by lots of zeros.
Still, it's fun to see how far the scale reaches.
If this is about Social Proof, and getting yourself in a Measuring contest one useful tool is the Benchmarking feature of Google Analytics.
Every website is different, so in case you are curious to see how other people in similar industries, geo graphic location or other metrics this is quite a useful tool to know things like 'Yeah, SEO is a good channel for us. Social, not so much.'
The "How Much Traffic Do You Need To Make $100,000 With Google AdSense" could be another scale
lot's of talkers on here. haha. Here's the real scoop. It depends on your goals. For businesses, traffic is somewhat irrelevant. Focus instead on conversions. For the ego, traffic is nice. Regarding what other hard working people are able to achieve...it's absurd to compare anyone on here to google or facebook or wikipedia. Very few websites in the whole world get 1 million hits. 100/month is a good start. 1,000 is a great start. 10,000 is damn good. 100,000 is holy poop super duper amazing. 250,000 is 'Fa-get about it!'
I think it depends. If you have a niche website with 10,000 monthly visitors, this could be a lot of traffic, too.
I've just broken down Nicks answer for <100,000 uniques as I think it needs expanding a bit :)
50,000 unique monthly visitors (a pop)
A healthy amount of visitors and showing the signs of value
25,000 unique monthly visitors (a buzz)
10,000 unique monthly visitors (a fizz)
Signs of potential for small sites
2,500 unique monthly visitors (a beep)
A blog/info site with a reasonable amount of interest
500 unique monthly visitors (a pip)
A very small blog visited only by a handful of people.
100 unique monthly visitors (a blip)
A tiny blip on the Internet.
20 unique monthly visitor (friends and family)
A website probably only visited by yourself and friends and family