I use Divelog
DiveLog because the Suunto (I have a Cobra) software doesn't run on a Mac, and I
will not run windows even if I could, although I can't, since my non-intel Powerbook G4 is still running fine.
I'm very aware of Macdive
macdive - home, I've pointed several queries here on SB to it, and can imagine it in my future because the support for Divelog going forward looks pretty iffy. I haven't migrated because I haven't yet needed to, I'm happy with Divelog, and because of the clumsiness of Macdive wrt handling multiple divers (my wife also has a Cobra, and I do her uploads).
I also saw a post recently
http://www.scubaboard.com/forums/computers-gauges-watches-analyzers/367755-dive-manager-mac.html that says Suunto will port their SDM to Mac, available this spring. Nothing else on that on the Suunto site, or found by google search, but I'm keeping my eye on it as another option.
+++++++++++1
... I like having 2 copies of it somewhere. Case in hand, one of my logbooks got soaked on a dive boat when someone I was diving with didn't fully close the dry bag. Soaked to the point of no recovery. Bought a new book and transferred everything back into it from the Oceanic software log. Saved the day for sure!
I've mentioned this before, but it bears occasional repeating. I also keep a paper log where most of the info and all the notes go, because I don't usually take my laptop on dive trips except Florida. At the end of each trip, I do a scan of the paper log to pdf using my HP inkjet multifunction printer. At 300 dpi b/w it's very readable, and two logbook pages fit in a nominal scanned page at 1 MB per two dives. At today's storage densities for disk/DVD/usb flash drives, that's almost no space at all. The scanning takes maybe a minute per dive for a trip, counting the setup, file manipulation, etc., for say a trip of a dozen dives.
Both the scans of my paper log, the Divelog database, and print-to-pdf of the Divelog database, get backed up regularly with all my other digital life.
I also keep the pdfs (both scans and Divelog) on my iPod Touch under Air Sharing
Avatron Software: Air Sharing , and I do take that overseas, so my dive logs are always with me.
As for Charlie's comments, maybe someday I'll get tired of computing my SAC or looking at my profiles, but at this point in my diving career, I still find it illuminating and interesting to look at that.