What uses are you considering? In some instances such as games, the desktop will likely 'cream' the laptop - in others such as CAD or heavy video editing, the i7 should take the advantage.
The desktop has the advantage of upgrade/expandability which is extremely limited in any laptop
not sure where the other posters are going, talking about ugradability!!
to answer your question, yes, a desktop i5 3570 will outperfrom the top i7 mobile (3610qm) purely on clockspeed alone, the i5 being clocked at 3.4 and 3.9 turbo, the i7 mobile being clocked at 2.3 and 3.3 (turbo). Despite having 8 threads the i7 3610qm does not perform in games as the i5 3570k would. In other applications where threading may effect the outcome it may make a difference, as the i7 has 4 cores with 8 threads, but even still the i5 is one of the best CPU's available even when compared to the high end extreme CPU's for most normal tasks.
It depends on which two CPU's you're comparing, but for the most part the desktop Core i5 will be faster in tanks like gaming while the Core i7 will take the lead in converting, compressing and other intensive things.
According to this, a desktop i3 will circulate around a laptop i7. Not surprising though. Desktop CPUs doesn't suck about three to five times more power just for fun, especially not in a world where we're supposed to save our resources. Or do you really believe that something like a Samsung S4 will kick the ass of a desktop Core 2 Quad, which it's surely unable to even power on with five connected batteries?