Forgetting Mother's day is unforgivable. Not because the day is sacred or anything, but because unless you live in a cave, with you fingers in your ears...you can't help but be reminded of it 100 times a day. Birthdays as they are not marketed as heavily can more easily be forgotten. So my point is, even if you do remind him of Mother's day, if he didn't get the hint the first 1000 times he was reminded via the general media, your reminder won't resonate either.
I'm a pretty forgetful guy, things don't get done by me in all kinds of ways, but I usually do pretty good in remembering birthdays.
One thing to consider regarding birthday reminders.... he may have planned a surprise and your reminding him of the upcoming date might ruin his plans...its happened to me
