I have a tech blog (PR1) which is around 4-5 months old. A month back, the blog was getting good results in Google SERP with around 40-50+ unique visitors and less than 5 from Yahoo. Now the situation is almost reversed. I am getting around 50-60 uniques from Yahoo and just 10-15 from Google. My blog used to rank at first position for some of the keywords earlier on Google. Now it is not even coming on first page for some of them. Also during this duration I changed the permalinks of some of the categories in my blog. Google's Webmaster Tool was showing me around 20 errors because of this, which is down to 2 now. Can someone please help me explain why is this happening ?