Comparing a mouse to a microphone is about as valid as buying a red car because you once were in a red car and it was pretty fast. An USB mic is a regular, analog microphone with a cheap one-way audio interface bolted on. In other words, the main problem with USB mics tends to be that while they're easy to use as such, they're most often extremely cheaply built (consider the fact that for the price of an already cheap microphone, you're also buying a microphone preamp, an analog to digital converter and an USB audio interface), and you can never use the mic in any other way than through USB straight to the computer. That's not to say an USB mic can't be good, in theory - but most of the time they're just not. XLR doesn't make a mic better, but it's a lot more flexible, because you don't have to buy a new mic whenever you want to, say, buy a nicer mic pre or hook it up to mixer or effects.
All that said, if you want a simple vocal solution, and know you won't be upgrading it or doing anything else ever, go ahead and buy an USB mic. They're decent enough for someone doing podcasts for example.
