And this is their form letter that they keep sending:

Hi,

I am contacting you from the Microsoft Corporation and its Internet search engine Bing (http://www.bing.com) in regards to your robots.txt file at http://poorbuthappy.com/robots.txt. Our customers have alerted us that your site was not visible in our results and we have discovered that you are hiding your site to our search engine crawler, named msnbot, via your robots.txt file.

We would be pleased if you edit your robots.txt file to allow our search engine to index your content which additionally will increase traffic to your site via our search results. The only step needed on your part is to remove the following restriction for msnbot within the robots.txt file.

User-agent: msnbot Disallow: /

Note: In October and November we transitioned our crawler name from msnbot to bingbot. You can edit your robots.txt using msnbot or bingbot as we will still honor all applicable robots.txt directives, including those specific to msnbot. http://www.bing.com/community/Site_Blogs/b/webmaster/archive/2010/09/03/bingbot-is-coming-to-town.aspx

If you feel that msnbot is crawling your site too frequently, you can use the crawl-delay directive in robots.txt http://www.bing.com/community/Site_Blogs/b/webmaster/archive/2009/08/10/crawl-delay-and-the-bing-crawler-msnbot.aspx

For more information about robots.txt please go to http://www.bing.com/community/Site_Blogs/b/webmaster/archive/2008/06/03/robots-exclusion-protocol-joining-together-to-provide-better-documentation.aspx

Our Webmaster Central website (http://www.bing.com/toolbox/webmasters/ ) can assist you further in obtaining the best results possible for your business or website.

If you have further questions please let me know.

Best regards, Name

So my question: should I let them back in?