I am using a Katana 600 as my first bike. I think it serves its purpose fairly well. Here are some of my observations:
The bike is very heavy, which is generally seen as a downside. This probably means you're more likely to drop it, but it'll help with your low speed skills when you upgrade to a new bike.
Above 7000RPM or so, the Katana will make more power than you need on the road, especially as a beginner. Down low, it can be rather tame (compared to supersports). This is good for the simple fact that it is easy to control yourself. You'll learn more about staying in the appropriate gear to generate power than you would on faster 600s.
The engine is rock solid. Repairs are simple. Models barely change between years, so parts are cheap and easy to find.
Very comfortable. The riding position on the 750 is a little less aggressive than the 600 as it's more touring-oriented, but my 600 is super comfortable. I can do hundreds of miles in a day without becoming very sore.
I ride with a GSXR1000, R1, ZX7R, SV650S and have never had trouble keeping up with them in real world situations.
Basically, it's a fairly decent beginners bike IMO. If you don't mind buying a used bike and selling it in a season or two, try a Ninja 500 or a Suzuki GS500F or SV650S. It's lighter, ample power for a beginner with his head screwed on straight, and easy to obtain parts and work on.
I think you said in your other post that you were going to buy a new bike. I don't reccommend that at all, unless you can pay for it with cash up front. Know that you can call insurance companies as many times as you want and bug them for quotes on different bikes (I did).