It's more problematic for those that include Ruby extensions in C, but fixing a library to make it 1.9-compatible is not generally that onerous a task (the major exception to this is string encoding, which is fine in simple cases but a complete nightmare in anything complex). If enough people just write patches for a couple of gems they use, everything would be 1.9-compatible soon enough. rvm lets you install all the different Ruby versions you'll need for testing easily enough.
