First week of May I was getting 530 organic visitors a week. Its a new blog and my traffic has increased every week at a good progress. 2nd week of May I dropped to 480 organic visitors and this last week I am down to 100 organic visitors. I have more than doubled my pages. Only thing I can think of that I have done differently is upgrade Wordpress to 2.5.1. Could a bad install affect my traffic? Please help!
All of those were Google searches. I am wondering if the last Google update affected me. I am still ranking high on those long tail keywords though.
An upgrade won't affect your rankings so long as you use the same permalink structure. Google tends to rank new blogs high until their algorithm figures out where your site belongs in relation to other similar sites...
Make sure there isn't a problem with your URLs. Go to Google and type in a long tail that you know you are ranked for, then when you see your site, click google's link and make sure it goes to your site without any problem. Also, use the XML Sitemap plugin and register it at Google Webmaster tools. This way Google will send you warnings if there is a problem with your site. It is a great tool, since they'll tell you if there is a problem with accessing your pages, or many other issues.