I think that perhaps Mathew is talking about the GDI object limit. At least under Windows 2000 and earlier versions (I'm not sure about XP) there is a firm limit of 16K handles that can be allocated system wide - regardless of your particular specs (ie adding memory does not help). When this limit is reached weird stuff [1] happens which can only be fixed by a reboot.
Any object that allocates a handle under Windows (pens, brushes, dc's, etc) consume those resources and if you've got a graphically intense GUI using a greedy GUI library (ie one that holds it's handles for a long duration) that limit isn't too hard to break.
If you open task manager and select to view the "GDI Objects" column you can see how many objects each process uses.
If you, or anyone else, wants some more info or help please let me know because it was quite a difficult nut to crack!
Googling for "gdi object limit", particularly in groups, will reveal a heap of stuff. However, I've found only a few official documents that describe the issue.
In practise the FOX GUI users group have found that the values are as low as a few thousand, or less if you are dealing with bitmaps. This may still sound like a lot, but if you are allocating a handle to every line on the display (plus any offscreen handles - eg caching a few hundred thumbnails), you can quickly run out. Mathew