Is there anything official as to the maximum length that Google permits for a meta description. From what I can gather it looks like 150 characters, just haven't found anything official.
That used to be the number I always heard (150 characters in length).... but I also have been told that Google no longer gives the Metas of Description and Key Words any weight in the overall algorithm which determines how your KW are sorted in the Search Engine. They WILL penalize you for spamming your KW (repeating the same words). And maybe an overly long description would dilute the content being crawled. I know almost certainly that the Title tag is still very important.
this is good reading material about "Create good meta descriptions" - http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=35264#1
There is no maximum length, obviously you can have the tag as long as you want. The recommended length would be the length displayed in search engine results Google displays 160 characters The main issue with meta tags is lost They need to be natural and enticing to search engine users, they also need to contain (without spamming) page relevant keywords. The idea is to find the right balance between Meta tags Headers Content Alt Tags URL structure
The meta Description is important because it gives you control over the text that appears under the blue link on the search engine results pages.
If your URL is targeting a 1,2, or 3 word keyword phrase then I would suggest keeping it under 145-150 characters. Last I checked Yahoo! truncated around 145 and Google around 150. Recently Google announced that for very long tail keyword phrases, they will display much longer snippets (which sometimes is your meta description element assuming it contains all of the keywords in the user's search phrase). I've seen them display snippets as long as 300-400 characters in length for very long tale phrases. Meta description elements are ignored by Google for ranking purposes, but they can show in the SERPs as the snippet IF your URL does not have a DMOZ entry AND all keywords from the users search phrase can be found in your meta description element. When shown as the snippet, even though it doesn't affect rankings at Google and certain other engines, the meta description IS important since a good one can greatly increase your click-thru-rate.