I have another - maybe less noticable issue, not sure if it's related.
I have noticed that almost on all my prints, there's a small but noticable imperfection always on one of the sides (corners). I tried to make some photos. Notice that always on a particular corner / side it seems as of the layers are not perfectly above each other. What could cause this? The other corners look pretty good. This is noticable even on small prints, so I'm not sure if it's leveling related.

Compare DSCN4193.JPG and DSCN4194.JPG. You will see that the two corners are different. Also compare DSCN4195.JPG and DSCN4196.JPG. Here notice that on the first photo, the light breaks at two lines, one is the real reflection of the light on the cylinder, the other is the imperfection. Then see DSCN4198.JPG. Here this imperfect corner is also visible.

Thanks!

I would suggest, if you need to print such small items in PLA to look into adding a cooling fan to the print head like these,

http://www.thingiverse.com/thing:20876

http://www.thingiverse.com/thing:30721

Something like that will actively cool the print while printing and solve at least some of your issues.

Also possibly your printer could be over extruding,  I know this is not your printer he is working on, something like this could help.  http://www.youtube.com/watch?v=JZGdMc2ebPo

Have fun and keep trying.

4. Red PLA tower (square): thing:122223
- Again the top is melted together. Scaled down to around 3 cm in height too.
See DSCN4185

I would realy appreciate some pointers, as I'm a newbie to 3D printing.

Thanks!
Bence

I have recently bought a chinese made 3D printer (Come3D C120, google it, I cannot post links for some reason) which works pretty good. I have made my first print with this model: thing:31313 (again, I cannot post links for some reason, from now on, this will mean a model on thingiverse)

It came out quite nicely.
Then I started printing other, more detailed stuff, and there I have some issues. I have already tried leveling my printbed with the paper method and I believe it's not bad, but if you say that my print issues are still related to the unlevel printbed, I can try tweaking it further.

Generally it seems that using the red PLA works much better than the blue ABS that I have purchased from the same manufacturer (Come3D). Is PLA generally better or maybe it's just a coincidence or other factors?

I'm printing using ReplicatorG 40 with the profile Thing-O-Matic HBP Strepstruder MK7 (this is what the manufacturer suggested), Gcode settings Thing-O-Matic slicing defaults, parameters:
- raft
- no support material
- 10% infill
- layer height 0.3mm
- no of shells 1
- feedrates 30
- temperature 200 for PLA, 210 for ABS
- filament diameter 1.75
- extruder nozzle 0.4mm

Slicing engine Skeinforge 50. Printing now from S3G from SD card.

My concrete issues with pictures:

1. House printed with red PLA: thing:33972
- Here, apart from the fact that the printing has stopped at the end (ReplicatorG reported a communication error, I guess I will always have to use the SD card printing approach) is that under the windows, the material drops. It's probably not that bad and maybe support material could work (although on such fine detail, maybe I cannot remove the support material). See DSCN4187 and DSCN4186.

2. Blue ABS tower: thing:122129 (scaled down to around 3cm height)
- This is where I have the most issues. The pictures speak for themselves. The lines are just bad. During extrusion it seemed that the extruder pushed down the previous layer it has printed, but at least it was touching it considerably. Before the print, I tried to calibrate the extruder to the center, and so it just touches the printbed. And the other print using PLA came out quite fine, using the same calibration coordinates and settings. So not sure if this is calibration related.
See DSCN4181, DSCN4182, DSCN4183.

Thanks and best wishes,
Bence