I find it invaluable at work. The first thing I do every morning is empty the tickler out for that day and all days up to the next time I'll be in the office. The kinds of things in there:
- printed out agendas for meetings/conference calls
- directions to meetings/airplane tickets etc.
- information on upcoming meetings/seminars I have not yet decided whether or not to attend
- information I like reviewing regularly (e.g., I may put it in the monthly folder for two months from now and when I get to that month I decide when/if I want to review it again)
- occassionally, everything that was on my desk the evening before (when I have to run to catch the bus, I still want a clear desk the next morning)

As others have said, you could keep all of this electronically and/or have reminders in your calendar while storing this information in your reference files, but the tickler works really well for me.

I tried it at home but I don't regularly look at it there, so I've given it up. I don't seem to have enough paper at home to make it worth developing the routine. So I will put every item on my calendar or a next action list - this way I know I'm not missing something.