If you don't trim the bottom on a regular basis, you won't elminate the layers.  But there's no reason why you have to do it any more often than absolutely necessary and by just trimming the damage, you limit how often it needs to be done.  I would suggest you keep doing what you're doing and every time you add a couple inches of growth overall, trim a half inch from the entire length.  By trimming the splits regularly you will be able to go longer without trimming the length, and by trimming the length occasionaly, you will keep your hair in excellent condition overall and will eventually elminate all the layers.  Patience is *really* the issue when it comes to growing out layers... it's a tough job!

There's not much to trimming hair that's one length but layers can sometimes be tricky.  I'd do a lot of research and see if you can't find a professional who specializes in long hair.  You might want to ask long hair friends where they get their hair trimmed.  Otherwise, if you know someone who has or loves long hair whom you trust *implicitly*, you can always try that route.

Personally, I have had my husband trim my hair since it was just below my shoulders.

Here's a site with a description of how to trim your own hair.  You might want try this!

http://members.fortunecity.com/feye/trim/

This post is ten months out of date but I thought this might help other people who are growing out layers or at least provide a different point of view.

Most people advocate regular trims when growing out layers but I disagree. This might not work for everyone but I have found that the hair tends to even up eventually all by itself. I asked my mother and a friend who have had long hair and they both agreed that this was also their experience. (My mother has very thick hair and my friend has quite fine hair.) My daughter also cut quite a chunk out of the side of her hair and you really can't tell the difference now. (Aside from her fringe and a 1/2 cm trim I once gave her that the only haircut she's ever had. I was horrified!)
The only problem with this method (lets call it the Leave it alone 'till it finally looks good method) is that you can have some awkward stages where all you can do is tie it back. My daughter certainly did! I've found though that when growing hair out from quite short that when it gets to just below shoulder length that I get curls which is nice.

That turned out to be quite a post! I'm aware that many (and probably most) people will disagree with me but I hope this may be useful to someone.

nice to hear that 

i decided i won't trim my hair more than needed until the longest part reaches classic length. actually i think the thin ends will bother me anyhow less when they are passed my waist. it's between waislengths and tailbone that they are the ugliest in my opinion. i quite liked layers at shorter lengths though, i even dislike the look of one length hair between shoulders and mid-back. i even liked them so much i had rather deep layers ... which are entirely ugly once gravity takes over and the hair becomes very straight.

I gave in and had my longest layer trimmed.  I'm actually happy I did, except I want all of my hair much longer than it is!  It seems I have less layers sticking out when I put my hair up.   I'm hoping not to do any more trimming for a long while now though.  Maybe I'll finally get to a true shoulder length  before it's all silver lol.