The company I work for in the BVI's keep kayaks strapped to the lifelines+stanchions just about half way up between the shrouds and the bow pulpit (50 foot beneteaus). paulK has a good point, it's not great for rough weather. However I have made a few trips across the anegeda passage (BVI-St.Martin) with the kayaks like that and through some squalls..they were still there in the morning.
Here in Long Island Sound I've seen boats keep them outside the lifelines to save space...I would never sail in any moderate winds like this, but for careful cruising they're nice I guess. Garhauer makes a rack for them that bolt onto the bottom of the stanchion...http://garhauermarine.com/catalog_process.cfm?cid=58