<p>Our team (5-10 developers)  plans to <strong>adopt Subversion</strong> for our .NET (Visual Studio) projects/solutions (VisualSVN Server, TortoiseSVN / VisualSVN).</p>

<p>What is the best way to <strong>organize a new repository tree</strong>? Is it okay to use <em>one big repository</em> or is it better to create <em>different repositories</em> for every solution / product line etc.?</p>

<p>Our projects can be categorized this way (example):</p>

<ul>
<li>Main Product Line

<ul>
<li>Main Web App

<ul>
<li>Library 1</li>
<li>Library 2</li>
<li>...</li>
</ul></li>
<li>Windows Client</li>
<li>Another Windows Client </li>
<li>Windows Service </li>
</ul></li>
<li>Tools

<ul>
<li>Tool A</li>
<li>Tool B</li>
</ul></li>
<li>Product Line 2

<ul>
<li>Software 1</li>
<li>Software 2</li>
</ul></li>
<li>Product Line 3

<ul>
<li>App 1</li>
<li>App 2</li>
</ul></li>
</ul>

We use one big repository, and just have everything structured in subfolders (/project1, /project2 etc) and that seems to work fine.
The Apache project has a
huge svn repository
and it seems to do OK for them! :)
In terms of organisation, the structure you gave looks quite reasonable. I think anything goes, pretty much, so long as it's rational (i.e. mixing up every single tool with every single project is probably a bad idea etc). So pick something which works for you (tools/, projects/ etc). Subversion has pretty good support for moving things around in the repository, too, so you can always change if necessary.