.NET Framework is actually the standard for Microsoft's development
world and I think that few of you have again machines with the old generation of
Visual Studio Tools installed (maybe this is justify only if you have old
customers that needs some special maintainance of previous projects).
Unfortunately, I think that you've also some customers that have
systems not always so updated (a so common fact), so one of the biggest problem
with .NET Framework is always to say to your customer that ".NET Framework
is an important piece for the future Microsoft's technology and it must be
installed as soon as possible on your systems!". 
Lots of customers don't have big problems to update their systems or to
install the .NET Framework runtime, but sometimes you don't have this fortune...
If you work with big customers (big public entities or big industries for
example) that have an IT infrastructure built on the past, well working and that
satisfy a big amount of operators every day, saying to the IT department that
you need a little changement on their machine configuration is always a big
problem.
If someone of you have these types of experience (I see it every day) I think
that lots of time you've see machines like this:
(with nothing installed) but what you need is a machine like this:
where the .NET Framework is installed and running.
One of the biggest problem with the .NET Framework runtime is its deployment,
a very simple task to complete but always a problem when you've not the
permissions to do it and you need to involve other people (and other
infrastructure inside a big company) in order to complete it.
One of the problem I'm observing every day is that the .NET Framework runtime
is missing on lots of machines inside big infrastructures, simply because the IT
department normally don't know its importance (but without the runtime, you
can't execute any managed code).
Lots of time during my work I've to install and test applications remotely on
our customers and, in order to test the architecture of the installed platform,
I've some "self-made" applications that does particular testing jobs.
Unfortunately, lots of these applications are built with .NET (C# or VB.NET)
so... how can I use it on my customer's machine? Other times, I can have the
need to quickly build an utility to make a job to the customer's db and the
quickest way to build it is using Visual Studio.NET (always present on my
machines), but it's a problem if my customers don't have the .NET runtime
installed.
Do I need to always have Visual Studio 6.0 installed on a machine on my
office? 
How to avoid this problem?
Unfortunately there's no a clear response, but everyone must know that
actually the .NET runtime is a needs.
I'm not a fan of "brute force" methods, but if Microsoft will decide to force
the automatic update of all Windows systems by deploying the .NET runtime via
Windows Update, every developer will have less trouble and a more easy life