We moved to a much smaller house while I was pregnant (oh the irony!). Although I miss things like having space for guests and a home office for DH, here are things I DON'T miss:
a) cleaning more than one bathroom
b) cleaning bedrooms that aren't heavily used
c) having more spaces for *stuff* than I could mentally keep track of
d) having the excuse of all that space to buy crap I didn't really need at Target
Also, I like that in our small house DD can play with her dollhouse in one room, I can use the computer in another, and DH can work at the table and we're all sort of cozily together, not in separate parts of the house.