Catching base Exception class in .NET

Question

I keep hearing that

catch (Exception ex)

Is bad practise, however, I often use it in event handlers where an operation may for example go

Answer 1

I've been working a fair bit with exceptions, and here's the implementation structure I'm currently following:

1. Dim everything to Nothing / String.Empty / 0 etc. outside of Try / Catch.
2. Initialise everything inside Try / Catch to desired values.
3. Catch the most specific exceptions first, e.g. FormatException but leave in base Exception handling as a last resort (you can have multiple catch blocks, remember)
4. Almost always Throw exceptions
5. Let Application_Error sub in global.asax handle errors gracefully, e.g. call a custom function to log the details of the error to a file and redirect to some error page
6. Kill all objects you Dim'd in a Finally block

One example where I thought it was acceptable to not process an exception 'properly' recently was working with a GUID string (strGuid) passed via HTTP GET to a page. I could have implemented a function to check the GUID string for validity before calling New Guid(strGuid), but it seemed fairly reasonable to:

Dim myGuid As Guid = Nothing

Try
    myGuid = New Guid(strGuid)
    'Some processing here...

Catch ex As FormatException
    lblError.Text = "Invalid ID"

Catch ex As Exception 
    Throw

Finally
    If myGuid IsNot Nothing Then
        myGuid = Nothing
    End If

End Try