I would say, it depends what you call lots of drives.
Things like 4 to 8 drives (whatever their BIOS numbers, i.e. IDE or USB) would be treated without problems.
The compiled-in limit are 10 IDE interfaces, 15 disks, 64 partitions per disks (including extended partitions, i.e. 34 useable).
The real limit is that the number of "ways to boot", i.e. kernels and DOS/windows MBRs should be lower than 60, but it is true that if you want to analyse the max number of filesystems to search for all possible kernels and initrd, it will start slowly.
There is for instance no problem having Fedora, Ubuntu and debian distributions in both 32 and 64 bits installed on the same PC (i.e. 6 distributions in 6+ different partitions), plus kind of 10-20 iso images of live CD distributions.
One problem with other bootloaders is that when you boot from a USB key, some PC shift all BIOS drives numbers, so that number cannot be safely written in a static configuration file.
For instance, if you have a distribution on a USB disk, distribution containing it own /boot/gujin.cmd to supply its own command line to its own kernel, you can boot your PC with or without this disk connected; Gujin will automatically recognise that way to boot and display a line in the menu.
It doesn't matter if Gujin came from the hard disks or the USB disk.