Hello Loonhaunt (and the whole community, by the way ;)),
I'm also a newbie and had the same question. Since Aduino seems to be "some kind od C/C++" I've done my research on that languages and it seems to be applicable to Arduino.
http://www2.informatik.uni-halle.de/lehre/c/c_includ.html:
(roughly translated from German)The difference between <header_name> and "header_name" lies in the strategy used to find the include file.
<header_name>
This form specifies a default include file. The compiler will search for it successively in all default directories (in the order of their definitions). An error is raised if it can't be found."header_name"
This form specifies a user defined include file. It may be used with a absolute or relative path. If it can't be found, then the compiler will search for it the same way like if <header_name> is used.