I've had a subscription to Inc. for 10-12 years. I can attribute a great deal of time/money savings to things I've learned or found out about in Inc., especially regarding general management and HR issues. I consider it a solid investment. Granted, quite a bit of what they publish is common-sense type stuff, and their slant is definitely NOT towards the small tech startup...although I've bought a few companies I've read about in Inc. and I've discovered new business trends by reading it over the years. It's a great way to get a feel for the small business market, which is my primary customer base in many ways...it also helps me figure out when niche products/services I'm already following are likely to break out into more mainstream popularity. Many internet startup guys tend to have 'Silicon Valley goggles' on and they would laugh at the technical expertise of the average Inc. reader, yet the Inc. readers are often slightly ahead of the tech curve when compared to the broader small business market. Anything that helps you to get into the shoes/mindset of your potential small business customers is worth the time. Even if you don't market DIRECTLY to small businesses, you would be a moron not to be aware of their purchasing power.
You can also learn a great deal from the less 'glamorous' industries featured in Inc. - lessons that you can transfer to software startups in sometimes surprising ways.
Regarding the ads/advertorials: that is their business. The advertorials are marked as such. They are not going to turn away ad dollars unless the ad is clearly illegal. I wouldn't either if I were in such a competitive industry. I wouldn't judge, say, 37Signals based on the customers they accept money from...so I feel it would be unfair to do so to a magazine. You just have to think for yourself and view everything with a critical eye. Just like anything else. I don't think their ads unduly influence their actual editorial content.
I also read Entrepreneur magazine, which is even sleazier ad-wise (and I must say I lost respect for them when they started publishing the lies/idiocy of Robert Kiyosaki in an actual monthly column) but the occasional gems I learn more than make up for the time spent reading magazines like that and the sleaziness/crap factor.
I read almost every business magazine I can get my hands on (Fast Company, Fortune, Forbes, Business 2.0 before it was killed, FSB, etc. - as well as about 30 industry-specific business magazines.) I think the more you read, the more likely you are to understand business and to see new opportunities before others do.
I almost bid on Inc/Fast Company when they sold to Mansueto, but I knew I didn't have the time to follow-through on it. I now regret the decision not to at least bid.