silvercue I totally agree. I've been using Diarium for around three years now and it's been superb. It's even changed the way I journal and helped me to pull more memories out of what I'd written before using it too.
I was concerned about database size at first too, but with over 1,000,000 words, nearly 5000 photos, and a handful of videos, my database is just over 1GB and still runs smoothly.
Of course it's natural to be worried about an app losing support in the future, but the export features are pretty comprehensive, so if god forbid Diarium doesn't last, it's easy enough to save your entries.