I'm fairly new to all of this, but from the research I've done, I agree with the above.
I've read a diamond steel is used to actually sharpen an edge (i.e. removing material), and that a normal "honing steel" is used to maintain an edge.
I'm not sure if I'm over-doing it, however, from what I've read, I do a couple of light passes with a honing steel after I use my knives before I put 'em up for the day. This supposedly corrects the micro-damage done to the edge that happens from normal use, and aligns everything.
I've been happy so far, and with doing that, I'm hoping to avoid having to have my knives sharpened professionally very often. I know its un-avoidable in the long run, but I think of it as proper maintenance, just like making sure they never go in the dishwasher, and are clean before putting up for the day.
I'd say get a good honing steel and know your not removing any (or much) material from the edge. Diamond is harder than your edge.