Here's an example: When doing patent search, the USPTO gives you a simple search
[ _______________________ ] [<Search>]
and an advanced search. In both search forms, you can write things like:

[TTL/"Abrams" And Num/124587666]

But now you already have your search with Title and patent number. Why not give the user a new form dynamically created like this:
Search for [ ______________________________ ]
( ) and ( ) or Title: ............[__________]
( ) and ( ) or Patent Number: [__________]
( ) and ( ) or [________]:... [__________]
[<Add search line>] [<Remove search line>] [<Search>]

While we are at it: Lets make it more intuitive thus:
You can type: [Title=Mouse trap Author=Mickey]
or you could type: [TTL/"Mouse trap" And ATH/Mickey
or [Titel:Mouse trap and Author:Mickey]
and you'll get:

---------------------------------

Search for [ ] (x) and ( ) or Title: [Mouse Trap] (all words)
(x) and ( ) or Author: [Mickey___________________________]
( ) and ( ) or [________]: [__________]
[<Add search line>] [<Remove search line>] [<Search>]

DID YOU MEAN Search for Title: [Mouse trap and Author:Mickey] ========================