UPDATE: A post today claims to explain it all.

According to a post on AppleInsider , the apps in Snow Leopard are going to be dramatically smaller and more efficient.

This weight-loss regime is prompted by the need to slim Mac OS X down for the growing number of mobile devices, so RoughlyDrafted (the source of the AppleInsider report) suggests.

As the graphic below demonstrates, the new apps are significantly smaller; Mail.app alone loses 196MB, over 68% of its current size:

Who would have thought that Mail.app had so much weight to lose?

According to AppleInsider some of the efficiency comes from a greater centralisation of resources in Snow Leopard:

Among the technologies believed to be aiding the downsizing are Resolution Independence, which substitutes bitmapped raster graphics with smaller vector graphics files, and Localization, which extracts the plethora of localized language files from each individual application and instills them into a centralized container accessible to each application.

Mail.app users can also look forward to more complete text handling features like auto word correction, smart dash insertion and more. mail.app, apple mail, snow leopard, leopard mail, apple, localization, resolution indendence

James Eagan has updated his Attachment Scanner plugin for Mail.app, which checks messages for attachments, and when it decides one is missing, give you a warning before you send.

With the help of several translators, it will now scan for attachments in English, German, French, Italian, Spanish and Swedish.

The plugin is freeware and you can get the updated version from James’ web site .mail.app, apple mail, plugins, attachments, localization