Yup, it's Bento WinAmp now!

Just make EQ dockable on top of main window...

I am kidding, I don't use this WinAmp layout, but it's finally possible to make it look like that with all that stuff placed in top left corner (you just wouldn't believe how many people I know still use Winamp and refuses to switch to MusicBee or anything else just because "it looks different"). Though, I am glad this almost WinAmp style wasn't possible in 2.x version when I switched to MusicBee so I was forced to get used to MusicBee as it is and eventually to get used to much better and more useful layout than WinAmp-style had to offer, but this is cool anyway because of new MusicBee users, they have option to make it more like the player they are used to (WinAamp both unfortunately and usually) and then to experiment with new layouts, almost always better than WinAmp layout in any way it is arranged.
Anyway, I like this MB.V3 very much, it is way faster now, but there are some glitches here and there, but I am sure it will be all fixed by the release time. As for now I can make point to couple of them:
1. Double clicking on Album picture in Library, when Play Album option is selected under Panel Settings, will start playing that album, or sometimes will queue that album but start playing the song next to currently played song instead of adding album to queue without changing playback, even though it is set to Queue Last in Preferences>Now Playing>Now Playing list (in 2.5 it always queues last, both albums or tracks double clicked when Queue last option is ticked; I don't know whether this is by design or V3 accidentally overrides Queue last setting from Preferences)
2. Clicking on elapsed time in sidebar player won't change time from elapsed song time to remaining song time and vice versa, as it does in 2.x; not too much of importance, but it is a nice feature to have, and it worked in 2.x, so why not now
3. Lyrics part of Now playing bar is either picking it's looks from wrong part of theme settings or it is less contrasted by design. Same goes for wavebar and spectrum visualizer, they look different too in a bad way (I will attach those screnshots below). Wavebar and spectrum visualizes are set to 45px height in both V3 and V2.5 screenshot but they are different in height (see screenshot), while font of artist, album, etc. is equally sized. This might be due to skin incompatibility with MB.V3, I don't know.
4. Space usage is better in V2.x when it comes to track data like bitrate, file-type, path, rating, etc. as it is shown on screenshot in green rectangle; whole 2 lines of precious small laptop/desktop screen space are "eaten" by this data being placed under the album art. I do, anyway, appreciate that path of file is now a link that opens in Windows Explorer node, thanks for that very, very much! Just make it all on the right of album art and save some space as shown in green triangle, just like in 2.x MusicBee
5. Crtl + Mouse scroll resizing doesn't work in library to resize Album cover picture, scrollbar under Picture size option must be used right now instead and it is not as convenient as Ctrl + mouse scroll as we all are used to in V2.x and also browsers or Windows explorer
6. Narrow scroll bars are in weird bright red color (in this Dark.mod.Inminente skin that I use), probably an issue with skin, but just to let You know it probably has the skin incompatibility issue.
ScreenShot:

Well, these two more issues are more like feature requests, but I found them rather UI and UX tweaks/polishing inconsistencies, and it applies both to 2.x and 3.0 MusicBee:
7. Deleting tracks from Now Playing list shouldn't stop the playback as it does now (selecting all tracks with Ctrl+A or selecting them with mouse and pressing Del keyboard button). On the other hand, clicking List>Clear list would remove all tracks but it won't stop playback. I think these two actions are basically the same, so they should do the same thing, clearing list without stopping playback (very old WinAmp and other players habit again here).
8. Auto fitting Album Covers in Library makes it way to densed. It makes like 3-4px space between Album covers and I think it would be much nicer and easier to use if spacing is just a bit bigger, like 8-10px
Sorry for the post this long, but I guess You'd prefer to have all issues and ideas provided by one user under one post, as it is more easy to manage and follow. Just keep on great work!

P.S. Fell free to delete any part of this post You find unnecessary or PM if I can help in any way