Developers can submit code to OpenStreetMap in various ways, depending on what you are working on.
Basically we have three kinds of applications:
1. Applications where anybody can submit a patch and it will be more or less automatically used. This is the case for example with the tiles@home client, where you just apply your patch to the SVN, maybe add a message to the wiki pages, and it will be pulled by the clients without further ado.
2. Applications where anybody can submit a patch (and apply it to SVN) but, being a server application, the patch only becomes active when the server admin updates from SVN. Depending on the personal preferences of the admin in charge, pulling stuff from SVN may be standard operating procedure, or may be done only on request, and some might even have problems with pulling stuff from SVN because they never check in their changes ;-)
3. Applications outside of our shared SVN, like JOSM, where it is the responsibility of those with SVN access to deal with patches.
For supplying patches, it can be a good idea to email the key developers directly, you might get a patch in quicker. (Also, plain and simple patches will be accepted quicker, because for the more complex ones that may turn the software on its head if one is not careful, developers will need to do some tests before applying it.)