I want to integrate a flex application(running on different server) with my alfresco 3.0 share client? Any suggestion, direction, help is highly appreciated.
Look at the flexspaces-share.zip in the "FlexSpaces Share Components" section of FlexSpaces. This provides 5 Flex based site page components that provide the functionality of FlexSpaces inside the 3.0 Share application
Although the iframes reference an html file (that includes a SWF file) added to the share web app, you could use the same technique to refer to an html url outside of the share web app. See share/WEB-INF/classes/alfresco/ site-webscripts/org/integratedsemantics/components/flexspaces-all/flexspaces-all.get.html.ftl
(If you want your flex app on the overall dashboard or on site dashboards (instead as a whole site page) look at share dashboard components too)