I guess we are not the only ones interested in credit cards for sign up bonuses. InsideFlyer asked for opinion on the subject. Here is the reprint of their article:

Rick Ingersoll has many years experience as a mortgage banker, credit counselor and mileage hound and is an expert when it comes to consumer credit and maximizing miles and points. He is the author of frugaltravelguy.blogspot.com, an informative blog that he frequently updates with news about travel bargains, cheap fares and the latest promotions from frequent flyer and hotel loyalty programs. We recently asked about credit cards.

InsideFlyer: How long have you been maximizing your mileage and point earning by getting credit card sign up bonuses?
Ingersoll: About seven or eight years.
IF: What have you been able to do with all of the miles/points you’ve earned?
Ingersoll: Not all my points come from sign up bonuses but they have helped my wife Katy and I fly around the world in business class in 2007. We are flying again on Oneworld business class award tickets this spring and will be gone for 61 days in April, May and the first part of June, 2009, and 58 of our 61 nights are award nights paid for with miles and points.
IF: How much of an impact does signing up for many credit cards over a short period of time have on a person’s credit?
Ingersoll: I estimate an inquiry on your credit report has a two-point effect. Open accounts are more complicated to determine as it depends largely on your utilization of credit in relation to your credit limit, the age of your credit, the ratio of revolving and installment credit and the timeliness of your payments. I applied for 16 credit cards in one day in July 2007 and my top score went from about 732 down to 651 after I eventually opened nine new accounts. I had an average utilization of 49 percent of the available credit limit per card. After paying off those cards, my top score is now 769.
IF: What kinds of limits do banks have on credit card applications?
Ingersoll: It varies by the lender. The big two are Citi and Chase in regards to frequent flyer miles and hotel points. Citi to date has allowed applications with these approximate limits and there does not seem to be any really hard and fast rule. With Citi you can get two personal cards within 60 days the first time you apply, but after that it appears to be one personal card every 60 days. You are allowed no more than two applications for personal cards within a 60-day period and one business card within a 90-day period and a maximum of seven cards open at one time, but I’ve crossed that number at times. Chase, the other big credit card provider, has stopped applying for all practical purposes with only one bonus per type of card allowed, but they have lots of different personal and business cards. AMEX cards I have not applied for other than the Delta card with years between the applications and I got multiple sign up bonuses, but that could change any day or already be changed. I have been denied a second sign up bonus on the SPG cards. As always, it may work differently for you. The other players are Bank of America with the US Airways cards, which are apply for many, and Juniper or Barclays, which I have not tried to apply for. I would expect in the current credit environment that this may soon become a thing of the past.
IF: Any advice for those looking to earn miles/points from credit card bonuses and sign up offers?
Ingersoll: Three things:
1. Know your credit score and keep track of your credit. It is amazing to me the number of people I talk with who have no idea that there are negative items on their reports or other inaccurate information. Clean up your report by correcting incorrect information and read all you can on things that negatively effect your credit. Ask somebody who knows what they are doing.
2. Have a plan. Don’t just apply because you see a new offer. Make sure the sign up bonus is really of benefit to you and your travel patterns. For example, I’m 200 miles from a Southwest Airlines city. I don’t have a Chase Southwest Airlines credit card. It makes no sense for me.
3. Don’t be greedy. Every time you apply for a card an inquiry is placed on your credit report. Too many inquiries is a common reason for credit card denial. It may all seem like free miles and points, but your credit is a much more valuable asset than any sign up bonus you may get.
IF: Do you have any caveats about credit cards?
Ingersoll: I would not be applying for multiple credit cards if I had a major purchase planned within the next two years. I would not be applying for credit cards for sign up bonuses if I could not pay off my existing cards every month in full. And lastly your good credit is one of your most valuable assets.