I_am_learning said:
I don't get it. If the letter writer succeeds in convincing that the student is very good at labs then isn't it good enough? I mean, a part of the requirement of being a good fit for grad school is to be good at the labs. So, proof of one of the parts is coming from the writer. Other qualities would be proved from other sources.
Basically, you are saying,
"I don't know what you want from him as a grad student, but he is very good at the lab works."
won't work, even if being very good at lab works is a very desirable feature of a grad student.
Sorry if my ramblings didn't make sense.
In the reference letter forms that I've filled out, they are usually looking for an overall picture of the candidate. Usually they will include specifc questions along the lines of:
How does this candidate rank among his or her peers in terms of (insert quality X):
bottom 50% top 50% top 25% top 10% top 5% no basis for evaluation
There will be a list qualities such as scholarly aptitude, research potential, teaching ability, independence, etc. to which these questions apply, and then questions about the pool of candidates the referee is experienced with.
There is also usually an opportunity to write any general comments.
So when selecting someone to fill these out, you ideally want someone who is in a position to evaluate you in each category. It's okay if they can't judge you on EVERY one, but if there are mulitple "no basis for evaluation" boxes ticked, that's not going to do much to support your application.
Now, with all of that said, I realize that not everyone is going to have a research-based, long-term relationship with three different, well-respected full professors who have been mentoring graduate students for the last 20 years.
Ultimately you have to choose the best people from the pool of those willing to write you a reference letter.
There is no reason why a lab engineer couldn't write Bunbun3x a reference letter. It's not like the letter would be thrown out or the opinions disregarded where they are valid. Admissions committees do pay attention to the position of the referee though and will weight the opinions accordingly.
One thing Bunbun3x may want to do is simply ask how many reference letters this person has given in the past, and (perhaps subtly) whether or not they worked out.