I am planning on either upgrading my Mobo to a better one, or getting an H61 mobo + a better processor.
By the way, here are my current specs:
ASUS P8H61-M LE (i will be replacing this as well, since one of the 2 ram slots doesnt work anymore)
Inno3d GTS 250 (will be upgrading to a Palit 650 Ti)
Intel Core i3-2100
FSP Epsilon 600w 80+
G.Skill Ripjaws X 2x2gb (will be upgrading to an Avexir 2x4gb Core Series)
Coolermaster K380 PC Chassis
Deep Cool Ice Blade Pro HSF
from there, any cash you had planned on getting a new mobo can be re-allocated for a better GPU if you wish.
if you want more onboard USB 3.0, then a new mobo makes sense if you're willing to spend, but not a Sabertooth Z77 if you're going for an i5-3470. a B75/Z75/H77 will do you good for half to one third the price of the Sabertooth.
if you want to OC, then grab a 3570K and a decent Z77, say Asrock's Z77 Extreme4, unless the Sabertooth's build quality is a major turn on for you or you want to get into enthusiast level of OCing.
EDIT: Haswell will be using a new socket, so no, it's not backwards compatible.