Sweetpea, just make sure you stay away from any cups that are made from "numbers" 3,6, and 7. These so far are considered to be "unsafe".

Unfortunately tupperware will not disclose to you as to which numbers they make their products from, so personally i would stay away.

from thegreenguide.com:

Plastics to Avoid
#3 PVC
#3 polyvinyl chloride (PVC) is often used frequently in cling wraps for meat. However, PVC contains softeners called phthalates that interfere with hormonal development, and its manufacture and incineration release dioxin, a potent carcinogen and hormone disruptor. Vinyl chloride, the primary building block of PVC, is a known human carcinogen that also poses a threat to workers during manufacture.
#6 PS
Extruded polystyrene (#6 PS; commonly known as Styrofoam) is used in take-out containers and cups, and non-extruded PS is used in clear disposable takeout containers, disposable plastic cutlery and cups. Both forms of PS can leach styrene into food; styrene is considered a possible human carcinogen by the International Agency for Research on Cancer. It may also disrupt hormones or affect reproduction.
#7 PC
#7 Polycarbonate (PC) is found in baby bottles, 5-gallon water bottles, water-cooler bottles and the epoxy linings of tin food cans. PC is composed of a hormone-disrupting chemical called bisphenol A, which has been linked to a wide variety of problems such as cancer and obesity.