When choosing the root folder of my music drive, containing apx 450GB of music and importing it into the library it takes a while to import all the info. Fine. However, when opening the library it takes about 25 seconds to open it, quite unacceptable. Does anyone have good solutions for rather large music collections when using the library ? Other solutions apart from just creating a playlist and importing all the files into the playlist, which is what I am doing now ?

I am using 0.9 final with columnsUI and I love it, been using Foobar for a long time and its one of a kind.

If by "opening the library" you mean opening the album list (Menu:Libray --> Album list), you have a work around by using the album list panel.
Your 25 seconds will happen only once when Foobar is launched.

You could also use foo_browser. I use it because it allows custom sorting. And because it use a simple list view instead of a tree view it should be faster than the albumlist.

custom sorting?.. how's that different from what albumlist can do? anyway, i don't think you want to have thousands of albums in a single, flat playlist.. trees really are lots nicer there
but yes, albumlist panel (perhaps coupled with the view panel only on click 'hidden' function on if you don't like it taking away a bit of your playlist view should work.

It lets me sort the items in the list how I like, for example ignoring 'The' in the artist name. As for having millions of albums in a list, I only have artists in my list, clicking on one loads all that artist's albums into a playlist.

I do that with my album list:

$if($stricmp($left(%artist%,4),the ),$replace(%artist%,The ,)',' The,%artist%)

and I sort it like that with my columns UI as well.

Okey thanks for nice feedback. Will look into it. I understand that its a lot of data to process anyway, and just my playlist file is apx 25MB so whenever you deal with that type of database within the album list, itll take a while for the software to deal with it. I guess Ill just stick with adding the files to the playlists for now and not use the library/album list and its nice tree function atm.