If someone sends you flowers, and they come with their stems inserted in those nifty water tubes, here's a great tip for thoses times when you forget to clean your brushes (I know, you'd never do that, but I sure have):

Pour an inch or so of Murphy's Oil Soap into the tubes.  Thread the brush handle through the hole in the tube lids, then suspend the hard-as-a-rock bristles in the soap.  Don't let the bristles touch the bottom of the tubes and make sure the top of the metal ferrule is above the soap.  The tops of the tubes will grip the brush handles tightly.  Prop the tubes up in a container and let the brushes soak overnight.  Next day, clean as you normally would, and voila!--the brushes are as good as new.

I learned a GREAT new tip while teaching recently at Painter's Paradise in Delaware.  Cut a Mr. Clean Magic Eraser (the "off-brands" don't seem to work) into chunks and keep a couple with your supplies.  Oil paint smudges all over your painting surface at the end of a painting session?  Slightly dampen one of the chunks, rub over the smudges and voila--gone!  Don't rub too hard as I have a suspicion it could even cut through the dried acrylic background if enough pressure was applied.