In Options, go to Languages / C# / Formatting Style / Line Breaks and Wrapping, find "Wrap long lines" below "Line Wrapping" group and enable it, then set "Right margin (columns)" to the desired value. That's pretty cool, but how can one see which lines will be wrapped?
Meet Visual Studio secret feature: Guides!
As described in this blog post, you can play a bit with registry and make Visual Studio display nice dotted vertical lines at specific column:
- Open "HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\9.0\Text Editor" key
- Create new string value "Guides"
- Set its value to something like "RGB(192,192,192) 119" (columns in registry are zero-based)
- Restart Visual Studio
Now you will be able to see when your lines are too long, and probably make manual formatting before ReSharper will split lines at next reformat.