I also do a fair amount of Microsoft Dot NET programming as well, so I was looking at MonoTouch too. For me, I know C# fairly well so that wasn't an obstacle, but it really came down to price. You'll have to pay $399 (or $999+ if doing Enterprise development) for MonoTouch, and that's on top of the $99 Apple Developer fee that everyone has to pay if you are planning to sell your apps.
In the end, I just brushed up on my C and C++ skills and learned Objective-C and used the native Mac XCode, which is a fairly nice IDE.
So if economics play a part in your decision, Apple gives all the stuff you need for free (don't need to pay $99 to just download the SDK), while you'll have to pay for MonoTouch.
In either situation you're going to have to learn Objective-C/C or C# (at least for right now).
Also worth mentioning are other non-Objective-C solutions. There is also PhoneGap and Titanium which won't require you to learn Objective-C/C. PhoneGap uses HTML, CSS and JavaScript to make iPhone/iPad apps. Titanium also uses HTML, CSS and JavaScript, but with added options to code in Ruby, Python, PHP, etc.
There's also GameSalad, which I haven't used, but I hear it's fairly easy to use, and geared toward people who have limited or non-existent coding abilities.
I still see GameSalad apps being approved (an acquaintance of mine got his Ipad app made with gamesalad approved a couple days ago) so I'm thinking Apple is, at least for now, letting people use GameSalad, Phonegap, Titanium and other 3rd party compilers. Apple's new approval policy restrictions seems for the most part just targeting Adobe's CS5 Flash to iPhone compiler. But who knows, Apple could change policies or reinterpret existing ones at anytime. So far they seem pretty lenient, as long as it isn't Flash/Adobe-related.