Always listen to people who know what they are talking about!

My printer doesn't yet have a heated bed, although I expect I will add one as soon as I get the machine working to my basic satisfaction. I am printing 3 mm PLA (as most resources seem to suggest that PLA is an easier material to get to grips with than ABS, and it doesn't absolutely NEED a heated bed). The RepRap Wiki and other sources strongly suggested using "blue tape" http://reprap.org/wiki/BlueTape on the print bed to get the printed objects to bond properly, with the most recommended blue tape being "Scotch 3M Blue Tape 2090". My local hardware store didn't have any Scotch brand "blue tape" when I went there a couple of weeks ago, so I bought a roll of generic paper-based painter's masking tape instead - BIG MISTAKE!!!!!

I found the PLA simply did not bond to the generic tape at all. I was able to get my early test prints to bond to paper which I bull-dog clipped to the print bed, but as I susbsequently discovered - this is (almost) OK for mucking around, but if you want to print something which is even half-decent, you absolutely MUST get a good bond between the raft / first layer and your print bed.

I went to a diferent hardware store today, and they had some genuine Scotch Blue Tape 2090, so I grabbed a roll. It was quite a bit dearer than the generic stuff I had bought earlier (although still very cheap compared to what I have spent on this project overall so far!), but what a difference it has made to the quality of my printed parts - WOW!

On the images that follow, one of my old 20 mm calibration cubes (printed onto paper) is on the left, while the same 20 mm cube printed on Blue Tape is on the right. All machine settings (firmware and software)  are identical - the only thing I changed is the contact medium on the top of the print bed.

Bottom Faces:

Top Faces:

Side View:

You can see that printing on Blue Tape gives me MUCH improved resolution overall: on the bottom face, the side faces, and the top face. I really wasn't expecting such a dramatic change to the whole print quality, just from having a better bond between the bottom printed layer and the print bed.

Do yourself a favour - if you are having any issues with the quality of your first prints (especially if you don't yet have a heated bed), I strongly suggest you use PLA filament and genuine Scotch Blue Tape 2090 - it certainly worked for me!