Since there's been some discussion about it here and other places, I thought I'd share what we came up with re: the Bonebreaker Rat Ogre and Look Out Sir!
I guess the notion that the BRO removed LOS! stems from absence of a note about it in the unit description, while the War Litter has such a note. This, coupled with its 4 wounds implying that it gets up to Unit Strength 5 (+1 from the rider), would lead one to think LOS! doesn't apply.
The trick is, however: the BRO isn't US 5. Here are the relevant bits from the Unit Strength chart on pg 71 of the BRB:
Now, there's some debate over the correct base size for the BRO; whether or not it should be 40x40mm or 50x50mm. I've based mine 40x40, since it'll rank up (and that's why I think they put the Pox Rat on a 40x40), but I don't think it's crazy talk to think it goes on a 50x50.
But I hope we can all agree that, although the BRO is "a prodigiously proportioned Rat Ogre," it's not going to be larger than a Dragon Ogre and it's not going to live in the same size category as a Stegadon or a Giant. That, by definition, an Ogre is going to be "Ogre-sized." (Because if it were larger than Ogre-sized, it'd probably be called a "Bonebreaker Rat Giant," right?)
That means it belongs in the first quoted category rather than the second quoted category. This means the BRO is US 3, +1 for the rider, giving us US 4. (As opposed to the second category, which would make the BRO US 4, +1 for the rider for US 5.)
As the model is merely US 4, it still gets to benefit from Look Out Sir!
3/8 UPDATE - From the new Skaven FAQ (dated 3/8/10):
Q. What are the Unit Strengths and base size of a War-litter? And what about a Bonebreaker?So, that settles it! (Until they change it.) I'm glad; it was an unworkably terrible choice at US 5.
A. For both models, we suggest using a Unit Strength of 3 (plus 1 for the Warlord), and a base size of 40mm square. However, do keep in mind that, as for all conversions, there are no strict rules about base size (other than: ‘Be reasonable!’), and that any forthcoming Citadel miniature might be different from this suggested size.