One thing I noticed when using ejunkie is occasionally some of the external javascript would take awhile to load. Not all the time, but sometimes. I personally think Ultracart is a much nicer solution for a 3rd party cart, also more expensive though. If you're selling digital products though and don't have to mess w/ shipping, fulfillment, setting up real payment gateways etc e-junkie is probably a better fit. Just my opinion, I've only worked with each on about 3-4 client projects each.