This may be a stupid question, but can someone explain per diem pay to me and how it differs from other types of pay? I really don't understand exactly what it is. I feel ignorant for asking this, but hopefully somebody can help. Thanks.

Think of it as a food allowance. And it REALLY helps. One of those +++Benifits that are worth much more then a cent or two more per mile. IMOP

Per-diem is the allowance for lodging (excluding taxes), meals and incidental expenses. The General Services Administration (GSA) establishes per diem rates for destinations within the Continental United States (CONUS). This is for transportation workers and people that travel abroad to offset the higher costs of eating and sleeping away from home.

Per diem (offered by a company) is money that is untaxed given to you by you employer. It permits the employer to pay less in social security tax (on the money given to you for the perdiem) and also lowers your tax burden right away. You pay less on social security tax, federal, and state.
Be wary though you MAY NOT claim meal expenses when you file your taxes in the spring if you opt for the company paying it to you through your weekly paycheck.
Currently if you filed taxes you would be allowed to write off 75% of 52.00 per day for each day you were away from home. Which is 39.00 per day (averaged for US, you can get a higher amount if you traveled out of the US) multiplied by the total number of days you spent on the road. So if you spent 300 days away from home you would be able to deduct $11,700.00 from your adjusted gross income (must use itemization to get this).
If you were paid less than $11,700.00 "pretax" by your employer then you could itemize the difference (what you were paid compared to what you could have claimed) your entitled to and deduct the discrepancy on your taxes. The flip side of this is if your employer paid you MORE than you should have received then it is your responsibility to declare the overpayment to the IRS when you file your taxes and declare the extra money as "untaxed" and subsequently pay the tax due.

I have found it is much simpler to avoid the per diem scheme offered by an employer and retain your right to claim the deduction when you file your taxes.

There are some that will advocate the perdiem works better through the company by showing less taxable earnings but this is usually due to alimony, child support, or garnishments that the driver wants to minimize.
Again the flip side of this is you have a lower "gross pay" amount and you may have difficulty applying for a loan with a decent interest rate with a lower gross income. Also paying less into social security will lower your retirement benefit (assuming social security is still around and viable when you are ready to retire). But to each his own I guess.

So, it's similar to BAH/BAS in the military? I think I'd be better off without it if I could go without it due to the tax/income reporting issues.

EXACTLY! I was going to say that, but I did not know if that would click. Thats exactly what it is in the military, per diam. And it really comes into play come tax time.

If the above is correct---and it probably is, because I've seen it mentioned in other posts as well, by similarly credible sources---it as an extremely important piece of information, because it means company per diem isn't going to let you beat what the standard meal deduction already gives you. Our company's 11 cpm per diem plan would easily push me over the $11,700 mark because I drive somewhere between 130K and 140K paid miles a year. 130K times $0.11 is $14,300, and 140K would be $15,400. The $11,700 figure is accurate for our company, because we get 1 day off for every 5 on, which translates into 305 days out per year (so 300 is a reasonable estimate).

In looking into this subject I thought maybe that's where you'd somehow be gaining a little in return for sacrificing the 2 cpm our company charges to get on its per diem plan. From all the posts I've been reading, it now appears you're basically just giving them 2 cpm for nothing at all in return! Unless you have something unusual to gain from lowering what your taxable income is recorded as, like maybe lowering your alimony payments or something like that.

The reason companies like to pay part of you wages as "per diem" pay is so they can save money. Per diem pay is not subject to withholding for taxes or Social Security/Medicare. The companies have to match you dollar for dollar on the money you pay into Social Security. So they save some money by paying per diem. Is this good or bad for the driver? It depends on you, your income and your situation. Someone getting close to retirement may be better off paying full witholding and boosting their income for the last years before retiring to boost there retirement income. Someone younger may be just opposite.