Update! Click here (Grid, Guides, and Ruler Shortcuts in Photoshop CC) to discover my favorite tips related to Grids, Guides, and Rulers in Photoshop CC.
Paths and guides are anti-aliased by default in Photoshop CS5 and CS6. This tends to make them appear thinner than in previous versions and for some, more difficult to see on high resolution monitors. To turn off the anti-aliasing, select Preferences and click the Performance category. Under Graphics Processor Settings, click Advanced Settings and uncheck the Anti Alias Guides and Paths option. Note: you won’t see the change until you click OK in both the Advanced Processor settings and Preferences dialog boxes to apply the change.