I've been using the Blue Microphones Snowball USB Microphone for the last two months and so far I have been rather impressed. I had been in the market for a new microphone for a little while; I was torn between the expense of a standard microphone and preamplifier setup and the ease of use and lowered expense of a USB microphone. Then only real drawback of a USB solution is the lower recording quality inherent to the devices currently on the market.
But the Snowball changed that; the recording quality rivals some of the lower end standard microphones, but the ease of use sets it in a category of its own. It really is a plug and play device and only requires slight system setting modifications to work on practically all home computers, whether Windows or OS X-based.
My only negative comment to date is essentially cosmetic: the shell of the microphone is made up of two sphere halves, connected at the midline and the resulting seam covered by a chrome-type sticker. This sticker has a tendency to come off regularly, though in most cases, it simply loosens on one end or the other. Nothing major and in no way does this impact the recording quality, but it's a visual annoyance nonetheless.
I can sincerely vouch for the worthiness of this microphone and for the price, I feel that it is an excellent value indeed. Highly recommended.