A window is "unused" if it has just been opened with Cmd+n. Previously a file opened from Finder would be opened in an unused window if one was available. This leads to problems with some Vim options, e.g. trying to open an encrypted file from Spotlight will fail. The code that has been removed also had some quite ugly hacks and it is not entirely clear whether the reuse of unused windows was entirely intuitive. (The "Open files from applications" option is not affected by this change.)
Do not pass arguments via DO since some options only work if the files to open were passed on the command line (e.g. "%" flag in 'viminfo'). Also, if a file is encrypted and opened from Spotlight the Spotlight search text is passed as input and it ends up being used as password for the encryption key, so the file opens up encrypted. The above problems still persist if Quickstart is enabled.
Rename Services so that it is clearer what they do when they appear in context menus: New MacVim Buffer With Selection New MacVim Buffer Here The latter Service now works in Finder on Snow Leopard (it was broken before). The Service "Open Selected File" has been deprecated since it does not seem very useful and it is rather confusing as to what it really does.
It is now possible to drag to resize a window to be larger than one screen. However, if the window size changes programmatically (due to scrollbars or toolbar hiding/showing, etc.) then the window will be constrained to fit on the screen holding most of the window. This is perhaps annoying but at least it is consistent with the way Terminal.app works (try opening a new tab when a Terminal window spans two screens).