I'm using DropCopy with Lion Developer Preview (10.7 build 11A459e) and it works for the most part.
Things that don't work:
- context menus (a.k.a right-click- or ctrl-click-menu) in finder do not contain DropCopy's options
Things that definitely work:
- sending files through dropzone
- receiving files
- sending messages
- receiving messages (as well as copying a message to clipboard or opening a received URL)
- "get clipboard" (both ways)

This is definitely a yellow exclamation mark (almost a green check mark) - by no means a red X.
By that I mean that the app is usable under Lion to a great extent

updated to Lion through Mac App Store
suddenly found, that DropCopy's menu items are now hidden behind "Services" (e.g. Secondary Click => Services => Send File via DropCopy). At least they're there ^^

One other bug that I noticed is that the Dropzone now appears only on one desktop (which afair was not the case with SL) and the setting "dropzone always on top" doesn't make any difference - it still disappears behind other windows.