The 'Brandy' update seems to have incorporated some pre-'Florida' results (another major update that occurred at the end of 2003), mixed with numerous new factors. Google stores its index on a number of data centers around the world. Since 'Florida', some of the old data centers were taken offline, and pundits believe that Google has kept the old SERPs (Search Engine Results Pages) in a preserved state for the last few months.

While we can only guess at what those changes were, the following are probably a good bet.

1. Increase in Index Size
   
   Google's spider, Googlebot, has had a busy few weeks -- at the time of the update, Google announced that it had massively increased the size of its index.

   This move was probably made to ensure Google made headlines at the same time as Yahoo! (for example, in this report in the BBC News, Feb 18th 2004). However, in order to increase the index size, Google may have had to re-include some of the pre-Florida results that had previously been dropped.
   
   

2. Latent Semantic Indexing (LSI)
   
   This is a very significant new technology that Google has always been interested in, and the incorporation of LSI has been on the cards for some time. If you are an insomniac, then Yu et al.'s paper is quite helpful in explaining the concept, but, in short, LSI is about using close semantic matches to put your page into the correct topical context.

   It's all about synonyms. LSI may see Google effectively remove all instances of the search keyword when analysing your page, in favour of a close analysis of other words. For example, consider the search term 'travel insurance'. LSI-based algorithms will look for words and links that pertain to related topics, such as skiing, holidays, medical, backpacking, and airports.
   
   

3. Links and Anchor Text
   
   Links have always been the essence of Google, but the engine is steadily altering its focus. The importance of Page Rank (PR), Google's unique ranking system, is being steadily downgraded in favour of the nature, quality, and quantity of inbound and outbound link anchor text. If PR is downgraded, and the wording of inbound links is boosted, this may explain, to a large degree, the position in which many sites currently find themselves.
   
   For example, most people will link to a site's homepage. In the past, due to internal linking structures, PR was spread and other pages benefited. Now, it is more important for Webmasters to attract links that point directly to the relevant pages of their sites using anchor text that's relevant to the specific pages.

1. Furthermore, Google seems to be using outbound links to determine how useful and authoritative a site is. For example, directories that are doing well are those that direct link to the sites, rather than use dynamic URLs.
   
   
2. Neighbourhoods
   
   Now, more than ever, has the question of who's linking to your site become critical. Links must be from related topic sites (the higher the PR the better); those links are seen to define your 'neighbourhood'.

   If we again consider the example of travel insurance, big insurance companies might buy links on holiday-related sites in order to boost their ranking. These businesses will actively invest in gaining targeted inbound links from a broad mix of sites. Consequently, their neighbourhoods appear tightly focused to Google.
   
   

3. Downgrading of Traditional Tag-Based Optimisation
   
   Clever use of the title, h1, h2, bold, and italics tags, and CSS, is no longer as important to a site's ranking as it once was. It is very interesting to listen to Sergey (co-founder of Google) talk about this, because he's the one usually quoted about the ways in which people manipulate his index. Google has taken big steps to downgrade standard SEO techniques in favour of LSI and linking, which are far less manipulable by the masses.

Google is also expected to add a browse by name feature.