LIMIT and 6.5

Greetings,

I was wondering if the new LIMIT command in 6.5 is implemented in such a
way that it does in fact improve query time and memory on large result
sets? I was reading a patch that gives the LIMIT command capability to
6.4.2, but there was a note that indicated that the query processor still
had to evaluate the whole query and only *returns* the indicated number of
tuples/rows. Is that the case with 6.5 also? If so, what is the use of
having such a command if it does not improve performance or save memory?
It is already possible (and easy) to just grab x number of tuples/rows from
a query since most of the time they are fetched in a loop anyway.

Thanks,
Matthew Hagerty