I use 1Password 3 on three different machines, with the datafile kept on Dropbox to keep everything in sync. This has worked brilliantly for ages, but recently I've been experiencing issues with newly added logins not showing up on my other computers. So, if I add a login from my home computer, it won't show up in 1Password on my work computer. It seems that, eventually (like...after a few days), it seems to fix itself. It's doing this with every new login I add now.
Apart from this, Dropbox is working absolutely fine, so I don't believe it's a problem on their end. If I open up the 1Password data file in my web browser, then I'm able to see the new entries, so it seems like the data is there, but just not being recognised by the main app.