Painting - Painting clean border lines

My wife has been painting many sections of the interior of our house lately. She does a wonderful job on almost everything, but she has some problems on the edges (where the wall meets the ceiling, around door trim, etc.). Any suggestions on how she can get a nice clean line or edge on the area that she has painted? She has used painters tape, but it doesn't seem to help much. There is often unevenness in the wall border or trim border, resulting in an uneven line.

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I don't like tape for that purpose. Having a good brush to work with will help a lot, add a little experience and it becomes a piece of cake. I would suggest a 2 1/2" purdy angle brush for starters. Load the brush and go close to the edge going closer as you move the brush along the wall. Painting mistakes are easily fixed and the more you paint the better your skills will become. :)

I think the best way is to do it by hand
A steady hand and practice, practice, practice
I think the tape takes more time and does not work as well

I thought there was a good description of "cutting in" in this thread:
http://forum.doityourself.com/showthread.php?t=229888&highlight=technique

Depends on what is on your ceiling - popcorn ceiling is the worst for cutting in. I agree with bthe others, a good brush and steady hand work. What I have done in the past is cut in the best I can, have a damp rag handy for paint touches on the ceiling, and then touch up the ceiling if there is still paint from the walls on it.

My wife has been painting many sections of the interior of our house lately. She does a wonderful job on almost everything, but she has some problems on the edges (where the wall meets the ceiling, around door trim, etc.). Any suggestions on how she can get a nice clean line or edge on the area that she has painted? She has used painters tape, but it doesn't seem to help much. There is often unevenness in the wall border or trim border, resulting in an uneven line.

I just wasted five minutes on a post that didn't make it due to network troubles.

Anyhow, a simple, easy, and attractive fix is to use quarter-round, shoe, or chair moulding to place along the ceiling/wall corners. It conceals any paint imperfections and is fairly cheap. It also tends to look considerably nicer than even perfect paint lines. It's also way, way, way easier than the practice required to paint near-perfect lines by hand. Unless you're a professional painter or plan to do A LOT of painting, it's not worth the practice.