I took a look at Droplr back in February and found it a nice, free, easy to use file sharing service for Mac and Windows computers. For those who want more, Droplr now has Droplr Pro. It adds quite a few nice bells and whistles, including private, password protected drops, and more storage. Users can upload files that are up to 1 GB in size, while receiving 100 GB of storage you can mange yourself. The free version, available through the Mac app store, limits uploads to 25 MB and gives you 1 GB of storage.
Pro users will also get a custom domain to share drops, instead of the d.pr domain current users will be familiar with. The Droplr developers now have added an iOS app that extends your file sharing from your iOS device. The app is free.
Droplr Pro is US $30 per year, or $3 on a monthly basis. If you're a heavy duty file sharer the Pro version is worth a look. I've used the free version quite a bit and found it reliable and useful.