I'm running four of DLink's Homeplug units on my network (two DHP-301 kits). I've been extremely pleased with the products since I bought them about three years ago. (I literally bought one kit, used it for a week and was so pleased that I bought another and told all my friends. :) ).
Your success will ultimately depend on the quality of the wiring in your home. For me, the performance in my bedroom (two floors above the fileserver) can be flakey at times and flawless at others. I rarely have problems otherwise.
For standard internet surfing/downloading you'll never see an issue with the homeplug technologies. The bandwidth they're easily capable of will most likely exceed your modem's bandwidth by a fair degree. For file transfers or streaming though, that's where it'll be a little slower that your standard gigabit network. (I regularly stream video from my fileserver to both a PS3 and an Xbox.)
One of the big reasons that I went the Homeplug route was so that I didn't have to run cable through the walls. I know my skill set and I'm not exactly a 'handy' person, so this was the perfect option for me.