True. I'm not opposed to the 4GB at all (jeez, how I wish the prices were $399 and $499 instead...that "psychological barrier" of $500 - and going beyond it - is just giving me fits).
I know that my 1GB shuffle is holding 266 of my all-time favorite songs, so I know that, give or take, I can always get roughly 250 songs into 1GB of space. If the formatted/OS and app-installed capacity of the 4GB is in the 3.2GB range, that basically leaves me just over two gigabytes for photos, contacts and any additional updates or apps (Apple or third-party) that may come.
If I felt confident that these apps were on the small, lean side, file size-wise (and I suppose they kinda would be, just by their very nature), I wouldn't worry (because I can always pull off songs and photos, and I'm not going to be watching TV shows on this, and certainly not two-hour movies). I just don't want any new apps or updates from Apple to be in the 800MB category, gobbling up space at a fast and furious rate, that's all.
My current iPhoto library is less than 200MB(!) (not having a digital camera allows that), so I'm not really worried about stuff from my end (music, photos, contacts...I can always control that, and pull back if I needed to)...it's strictly "is Apple going to release big-ass updates and apps that will make 4GB seem really puny before long?"
No way to really know that, I guess.