The technical issues are definitely not insurmountable. Mono, the free CLR implementation, had CLR apps running on iPhone years ago, and several commercial and prominent games were developed with Unity Framework (which is based on Mono). There was even a "MonoTouch" development profile for iP* for MonoDevelop, a popular Mono IDE.
So, not only are the technical issues solvable, but they'd been solved for years by the open-source clone of .NET.
Not all of them ... with both MonoTouch and Unity you need to have a Mac OS X running with XCode installed, otherwise you can't sign, package or test your application in the IPhone emulator.
If this announcement is about developing, packaging and testing iPhone/IPad apps with only a Windows workstation within Visual Studio, then that's certainly good news.
Not to mention that MonoTouch and Unity are legally both in a gray area right now ... because they are explicitly disallowed in the new SDK EULA and Apple hasn't mentioned their official position on them (AFAIK).
I want to clarify the legal issue, though. There is no (non-patent) contest on MonoTouch or Unity's right to existence; people are free to make iPhone runtimes, compilers, etc., as much as they want; the issue arises when developers deploy these techs, as Apple's new EULA is applicable only to developers. While the effect may be the same (no use), I think it's an important distinction.
So, not only are the technical issues solvable, but they'd been solved for years by the open-source clone of .NET.