Sharepoint is really good. But folks forget that its a complicated technology and although you can do some very cool stuff with it, it does get complicated very quickly.
It's been used as a blunt weapon time and time again to snatch applications away from Lotus Notes - and it does work well for simple applications. Discussion databases, project tracking databases. So far so good.
But when otherwise sensible people start thumping the table, drinking the MS cool-aid just a little too much and believe that a single Sharepoint developer can replace something like 50 man years of domino application development - say for a major fund management CRM and tracking system - you really have to step back and wonder how it's going to play.
Well, what happened is that the company has had little or no development on their primary trading platform for years, and after years of unsuccessfully trying to find this single genius Sharepoint developer capable of transforming tens of thousands of lines of code - well, you can guess.
It does take a long time, but the folks responsible for this sort of disaster finally do get put out to pasture. Its a shame that it takes so long.
So beware the curse of [insert other platform here]. You might very well get some tactical advantages, and be able to move portions of your business critical applications off your existing platform - but don't pretend it won't be a long, costly, drawn out affair, eh?