Jailbreak actually seems quite unimportant to me on the iPad, particularly the Wifi one, compared to the iPhone. I would use it for the inevitable ability to have more columns of icons on the springboard, which is sorely needed, and Categories until OS 4.0 comes out which is probably towards the end of the year as they seem to be prioritising the iPhone. Those are two pretty important features if you have a lot of apps - albeit not essential.
Bluetooth file transfer isn't that big a deal either, again that's more likely to be required out and about with the phone sharing things with friends etc rather than with the iPad.
Themes would be nice but the interface is not as boring as the iPhone one so it's not that important 🙂
File system access and AFP sharing are not really important as 99% of the time I used it for easy access to photos/videos or ringtones neither of which are applicable here.
But that's about it really for the Wifi version. The 3G version will benefit from SBSettings for quick access to 3G and GPS on/off toggles and for 3G derestriction etc.