this is probably common knowledge to some people but i would pass this along.
when you caulk/silicone/whatever a new tub, or recaulk an old one, fill it with water first for the weight. when the caulk dries and the tub drains it will raise up and compress the caulk leaving it intact. when its full again its simply in the relaxed position.
if you dont do this, when you fill the tub it will sink down a bit and it can pull the caulk away. stuff holds up better under compression than from being stretched.
hope this helps someone.
randy