You can write a PowerShell script(named ListWebUserInformationListItems.ps1) as following:
# Run with SharePoint 2010 Management Shell
$webUrl = Read-Host "Enter the web url"
$web = Get-SPWeb $webUrl
$list = $web.Lists["User Information List"]
$query = New-Object Microsoft.SharePoint.SPQuery
$queryCamlString = '<Query><OrderBy><FieldRef Name="Title" Ascending="True" /></OrderBy></Query>'
$query.Query = $queryCamlString
$userInformationListItems = $list.GetItems($query)
foreach($userInformationListItem in $userInformationListItems)
{
echo $userInformationListItem.Title
}
Then execute the script and input the web url when console window display the "Enter the web url" message.
Note: You can use SPQuery the get the User Information List items which are the users in this web application. The users are not all the users in the farm. And if you add a ADGroup to the SharePoint, you will add the only one SharePoint user to user information list(The SharePoint User stand for the ADGroup, the ADUser in the ADGroup will not present to the user information list).
The User Information List item title will display in the console window.

More over:
You can visit the "http://[your web application url]/_catalogs/users/detail.aspx" to view the users who are in the web application.

Hope the answer will help you