While optimizing a website for Google you always think how Google count your effort in spam tactics that violet their webmaster guideline. From 2005 Google was working on website penalty issue. Finally Google had included website penalty notification in Google Webmaster Tool.
In late 2005 Google started to send email notification to webmaster about letting them know about webmaster guideline violation. But due to number of spoof message outside from Google they took out that features before few months.
Now, Google webmaster tool is greater verified site owner, so if you want to know if your SEO tactics violating Google webmaster guideline then you need to register for webmaster tool.