Hi. There is a thread in the forum "Tips, tricks, and step by step guides" http://forum.xbmc.org/forumdisplay.php?fid=110 discussing how to use the plugin.makemkvbluray to stream blurays to XBMC for direct viewing, so you don't have to rip them. Apparently, some people have been having problems getting that to work. This post offers a manual procedure to sidestep those issues while achieving the same thing: enabling bluray disk viewing for XBMC. plugin.makemkvbluray automates stuff that you will do manually here, but until you get it working (or you want to select a main title that isn't the longest one) you should be able this procedure.
First, get and install MakeMKV. Be sure to enter a valid registration key (either the beta key http://www.makemkv.com/forum2/viewtopic.php?f=5&t=1053, or one that you have paid for).
The method covered here uses UPnP in XBMC. Start by going to to the System -> Network menu and enable "Allow control of XBMC via UPnP". Then go to the top level "Videos" header and select "Files". Type 'c' and click "Add Source", enter "upnp://" as the name for the media source. Click "OK". It will then ask you to set content. Click "OK". Exit XBMC.
Load up your bluray drive with a disk and fire up MakeMKV. Once the disk is recognized, click on the big green arrow. It will take a while for MakeMKV to do its thing -- up to 2-3 minutes. Progress is commented in the message window. It will show "Operation successfully completed" when it is ready for the next step, which is to click on the icon in the toolbar at the top that looks like an LCD screen with a radio telescope behind it. That should start up its UPnP server. When it says it is done, go back to XBMC.
Under the main "Videos" heading, click "Files" and then "UPnP Media Servers (Auto-Discover)". Click on the entry containing the name of the computer that is attached to the bluray drive (MakeMKV and XBMC can be running on separate computers in your LAN, or the same one -- your choice). Then navigate down to the title that you want to play. Click on it, then "raw.m2ts". After a few seconds you can sit back and enjoy your movie.