Just an FYI. There seems to be issues with m4a right now. The files play fine but the scanner is unable to read any tags.. at least with the m4a files I use to test. If you have a large amount of m4a files, stick with 0.17. It wont read them but I have gotten reports that things can get pretty sluggish in 0.18. If you only have mp3/ogg 0.18 should work fine.
The next update is going to be a big one and it should address the issues with m4a files. Also I successfully got gapless playback working with ogg tonight. MP3/M4A are a bit trickier so that may take some time, but I am making good progress.