Not feeling the VS love when you double click on a SLN? Was the SLN file maybe created in Orcas? Then you've got some notepading ahead of you...

Andrew Arnott - Why double-clicking on an .SLN file doesn't always launch Visual Studio

"...

Scenario

You have Visual Studio 2008 installed, but some Visual Studio Solution files (.sln) don't open when you double-click on them.  In fact, nothing happens.

...

The issue comes up when your .sln file signature (the first two lines of your file) don't match any known release of Visual Studio.  Visual Studio 2008 .sln files typically start with these two lines:

Microsoft Visual Studio Solution File, Format Version 10.00
# Visual Studio 2008

But suppose you have a .sln file that was created with a Visual Studio 2008 beta.  You might have a .sln file that starts with this instead:

Microsoft Visual Studio Solution File, Format Version 10.00
# Visual Studio Codename Orcas

When Visual Studio 2008 RTM reads this, it doesn't recognize its earlier beta versions' solution file signatures and just quits.

..."

Fire up notepad, edit the SLN replacing "Codename Orcas" with "2008" and you should be gold...