suggestions

[Guest]

File associations:
button for deselecting all extensions,
command line option for associating of SMPlayer with extensions,
choice between all users and current user.

IMHO, there should be no two different EXEs for portable and non-portable version.
There should be one program and some way to choose where to store config. files.

Playlist: default row height is too large (minimal height is good for long lists). It's apparently due to the size of indicator icon but a solution should exist.
It would be comfortable to have different commands under "+" button for recursive and non-recursive adding of a directory to the playlist.

Working directory of Windows program should be located in APPDATA, not in USERPROFILE.