Downsides to Intrafamily IM?

Frisky070802 writes "The NY Times has run a column on how many families now use instant messaging within a household, for instance to ask what someone wants for dinner. This is especially popular as whole houses get wired (or wireless) and computers are scattered throughout the house. This is the case at my house but I tend to be the only one who stays on AIM reliably. Can Slashdotters offer some personal experience, pro/con, with being instantly and constantly accessible to one's spouse and children? Does this tend to break down your 'personal time'?"