Having seen many entries on this I wanted to clarify one point about the delimiter \u2029 in Fast Search for SP2010.
The delimiter "\u2029" only works in the context of Pipeline Extensibility.
"In the input to the extensibility stage the special character U+2029 is used as a separator for multi-valued crawled properties".
In other words, in order to send a multi-valued CP to the Pipeline Ext we separate the values with the \u2029 separator in the input xml.
When processing the output xml we look back at the separator (UTF-8 encoded) to build back a multi-valued CP in the Document Processing.
To support single-valued CP with custom delimiter (i.e. ';') , you need to go through the Pipeline Ext as described here : http://social.technet.microsoft.com/Forums/en-US/fastsharepoint/thread/a4285ae0-c899-4c6c-ab24-032e70d4525d
Note: Inserting the separator in your content directly will not work since the Crawled Property sent to the Document Processing would still be single-valued.