one most important thing

right now they are accepting usa person application only

I'm not aware MSN accepts only US residents, either now or in the past.

Adcenter is very much like Adwords. The terms used are similar, if not all the same. So if you're familiar with Adwords, you should have no problems with Adcenter. The interface is a bit different and can get some getting used to but nothing nobody can't handle. They are similar in many aspects. In fact, they are more similar than different.

They ad sizes are the same: 25 for title but instead of two 35-character description lines, they use one 70-character line. They also use the same way to denote phrase and exact matches with double quotes and square brackets. They don't have Adwords new modified broad match however but they likely will in the future.

Adcenter has its rules and guidelines as well. A lot of them are similar to Adwords. ALL pay-per-click search engines have their equivalent of Quality Score. For most, it's simply your click rate. Your ranking, as with Adwords, is determined by multiplying click rate and bid. If you don't follow the rules in Adcenter, your ads will be disapproved and won't run, just like Adwords.

It may or may not be cheaper. Costs are still dictated by what competitors bid and their quality.

I've been using adcenter for a while now and so far its proven to be more profitable than when I was still with Adwords.

They don't have a quality system set up so your able to get away with a ton of things that would normally get you banned quickly on Adwords. You'll just end up paying more if your keywords aren't relevant to the ad copy and landing page.

One thing you'll notice quick with adCenter is that its slow and buggy, but I've managed to deal with it so its not too bad. The interface seems to be years behind Adwords. They also don't have a feature to rotate your ads evenly so split testing your ad copy will be a little more challenging but not impossible.

Like adwords Adcenter has a desktop software for those that need to upload huge campaigns. Its totally buggy and slow but it works.

One last thing, bid prices on Adcenter are about the same as Adwords. I went in there thinking they'd have cheaper clicks but thats far from it. Adcenter is better because it converts better.