After seeing some of the great results folks have had with heated build platforms (such as Hydraraptor's groups of pieces, I wanted to try one too. I'm mostly interested in cutting the warping of long parts, avoiding printing rafts, and experimenting with the nichrome wire.
Here's a photo of my build platform; I based it on Hive76's design that they're selling through Makerbot. I far as I could tell, they use a couple pieces of glass, nichrome wire, and silicone sealant to make their build platforms.
I tried the same, though I sealed all the wires between the two layers of glass with tons of silicone. I used the same 10 ohm piece of nichrome, soldered the ends to longer pigtails of copper wire. I then cut two pieces of 4" square glass with a glass cutter and straightedge. I used dots of silicone and carefully placed weights to get the wire in place. I also added a spare thermistor and wires for measuring temperature, then covered everything in silicone, added a spare piece of copper wire at the far side of the platform to keep the pieces of glass parallel (because of the soldered connections on the near side), then smushed the two pieces of glass together.
I also used a bit of Radio Shack pre-drilled circuit board for the circuitry to connect the thermistor to the spare A6 analog port on the extruder controller.
I found 16 inches / 10 ohms of nichrome wire isn't enough to get sufficient heat; it took around 15 minutes to heat the glass to 55 degrees Celsius, and while the ABS would bond to the glass at hotspots above the wires, the plastic wouldn't stick to the glass elsewhere, even if I made sure the glass was clean and free of grease.
Looks like I'll stick with my 1/2" plexiglass build platform I currently use, though I might take another pass at the heated build platform in a few weeks.
Also this weekend: my original extruder nozzle/heater died with a broken wire, so I made a new one from spare parts. The original one put in a fair number of hours. I also found that ReplicatorG version 13 (for the heated platform support) also is much quieter about moving the stepper motors - that was a nice surprise!