Last week I decided to try a few things to get the surface finish on the bottom of my parts smooth and high gloss because I was sick of getting a rough finish and the PEI sheet just isn't suitable for all applications. This may be obvious to some or may already be done by some people out there but being new to repraps, having only ever used big fdm machines, this was for me one of those things that has made a big difference to the overall quality of my prints.
I'll try to keep this simple and short so you're not reading all day. "UHU" glue the one that most people use for bed adhesion, and I'm told "Elmers Disappearing Purple" (thanks McSlappy) are both soluble in water aka H2o. After cleaning my plate for the umpteenth time in the laundry sink and being sick of reapplying glue yet again, I finally decided to throw my glue stick in a jar of water and have a go at brushing it on with a cheap 50c foam brush. I haven't looked back since! Not only does it take the hassle out of the application but you very rarely have to wash you plate, and there is virtually no cleanup required to the bottom of parts, I also haven't removed the glass from the machine in over a week. It leaves the base of the parts super glossy, sticks AND releases parts really well, even better than PEI IMHO, and works for ABS, PC, Bridge and probably many others that I haven't tested yet.
Basically you put the glue stick in not too much water, say about enough water in a jam jar to cover the piece of glue stick is enough to start with. You can leave it sit there and let it very slowly dissolve or you can give it a hand and shake it up a bit it doesn't really matter, either way you are looking for a milky white solution that is not too thick. Clean your plate first, calibrate to the clean surface if you need to and then stick the heated bed on set to whatever temp suite you, I use 85C. I use a 2" wide foam brush to apply it but any applicator will do, something that absorbs some solution and is as smooth as possible to lay down an even coat, maybe even a sponge if you have nothing else, so long as its nice and smooth. As the plate is heating up you want to apply an even but thin coat all over the glass, going back and forth, as well as diagonally across the plate and work the glue solution into the glass well without actually putting TOO much glue down. You may, like me find that you get a small amount of foamy type bubbles, this is fine just keep working it in, you want to do this gently and evenly as it heats up and try to keep your glue as thin and as even as possible.
Trial and error and you will work out the perfect thickness pretty quickly, it's not rocket science.
I'm really bad at explaining things usually so I'll let the photos do the talking and if I haven't made myself understood or anyone has any questions I can answer I'll do my best, hopefully this will be of help to someone. With a bit of luck a mate will chime in with a howto video to show the method in action... 
Gluestick in water, this is my mix before I worked out that less is more and added more water.
I'll try a box this weekend using dissolved purple disappearing. I've been using Aquanet on purple ABS and the edges of the box has been lifting, may be other problems contributing. Box isn't 7" x 7" though. More like 3" x 3".