First of all thanks for taking an interest in this Matt - I know how busy you guys are so that's much appreciated.
Michigan_nik & gpvillamil were spot on in that I don't feel it's logical to have thumbnails on all the time. For example, if I'm selecting from a list of artists I just want a list - it's much quicker to navigate. When I've selected the artist I'd like to see the artist's albums in Thumbnails. Once I've selected the album I want to see the tracks in a list.
Do you want this because of the performance of thumbnails on your system?
Yes and no. No because the above is a very valid point. yes because I'm surprised you say that thumbnail caching is implemented. If I view this VS:
album artist (auto) (grouped 4)
album artist (auto)
Album
...when I select A-C the thumbails start to build. If I page down it builds some more. If I page up it doesn't rebuild - it must have cached them. If however, I press left arrow twice to go back and then reslect A-C it builds the thumbnails again. As I'm using a 42" screen at 848*480 res the large thumbnail looks best. I think this is the key as to why it's slower to build the thumbs- too painfull for words.
I have 23K files and my VS are pretty simple like the example above. My album VS for example is separated using VS groups into a Single artist scheme and a compilations scheme - just to make it cleaner when browsing. I don't have any ~ modifiers in these schemes or the parents as I did some testing for you with Dragyn a while back and know that this affects performance.
I have 2 computers, a Tower and a new HTPC but inside they are pretty similar performance wise (different hardware though). My HTPC for example only ever runs MC, Powerstrip and Girder - nothing else. I have an ATI 9600 pro running at 8x AGP, Athlon XP 2200+, 1GB DDR 333 RAM. All latest drivers and BIOS.
But, going back to my first point I think it would be a fantastic improvement to Theatre View to give us the flexibility to have Thumbnails when we want them i.e. when it's most appropriate - not just for performance but for usability and aesthetics. It just so happens that a side effect of this would be a performance improvement too for many people. [edit - The great thing about MC is that the way it's view schemes are built it lends itself to easy customisation. With many other programs it would be difficult, cumbersome and complex to add this flexibility but with MC it's just another selection in the VS wizard].
Thanks again for your interest. Let me know what you think.