Some people take a higher hourly (taxed) rate in addition to a lower per diem while others keep more of a balance between the two. You can refer to the IRS website regarding per diem rates for each state if you're concerned about the amount they may be offering you. Scroll down about half way and then look up the city and state you're traveling too. (Reads: rates "Effective October 1, 2007 - September 30, 2008") http://www.irs.gov/publications/p1542/ar02.html#d0e335
Getting a higher per diem rate is not necessarily a bad thing. Afterall, that money is "taxfree". However, you don't want to accept a really low taxed rate (especially one that is below the market rate for what you do) as that could possibly be a sign that the company may be trying to avoid necessary taxation on their end, and that would be bad for you in the end. Hope this helps and good luck!