Don’t use Configuration.Save in scenarios where users might only have read and write permissions for the configuration file as UnauthorizedAccessException will be thrown if full control is not granted. More details are available in the following MSDN Forum posting.

ASP.NET offers several ways of mapping nice public URLs to cryptic internal URLs matching the actual implementation.

The simplest way is to match each public URL to its internal value. You can do this by either creating dummy pages which do the redirecting or by adding them to the urlMappings section of the web.config file (brought by framework 2.0). The latter solution is preferable because of simpler maintenance but both of them have the downside of being completely static (an entry is necessary for each mapped page).

A better solution is to implement an IHttpHandler or IHttpModule and do the mapping by calling HttpContext.RewritePath(). You could also change the requested page by using Server.Transfer() or maybe even Response.Redirect() but they have their disadvantages when used for URL mapping.

To avoid having to recompile your IHttpHandler implementation every time the mapping logic changes or extends you could configure it through a custom section in the web.config file. Regular expressions are a nice tool for defining such mappings as demonstrated by here (also check the comments) or implemented in dasBlog sources (check newtelligence.DasBlog.Web.Core.UrlMapperModule). You could even use UrlRewritingNet.UrlRewrite if you don’t like reinventing the wheel.

The following code returns the time when a web resource was last modified:

static DateTime GetModificationTime(string url)
{
   WebRequest request = WebRequest.Create(url);
   HttpWebResponse response = (HttpWebResponse) request.GetResponse();
   DateTime lastModified = response.LastModified;
   response.Close();
   return lastModified;
}

It’s quite a simple piece of code actually and very similar to a sample in MSDN. But maybe it will be useful to someone since a member of my developer team was convinced that there is just no way to get this information in .NET.