You should note the receiver will work with any new Logitech wireless device that uses the unifying connection so you will actually save USB ports if you buy new Logitech devices down the line.
As long as it uses a unifying receiver then it will work, each receiver can host up to 6 devices so effectively saving you 5 USB ports or from having to use a USB hub!
There is no lag, much like the other Logitech 2.4GHz wireless mice - it feels like you're using a wired mouse. The advantage of the newer darkfield lasers of course is they can be used on glass/shiny surfaces and track down to finer detail.
Been looking at this mouse myself and I'm still undecided. Struggling to justify the price.