Can Transcranial Magnetic Stimulation (TMS), or a magnets cap make you smarter? According to wikipedia, TMS is a bunch of magnetic fields directed to the brain which stimulates and activates neurons.


If I wear a cap full of magnets, will it stimulate my neurons? 
If yes, will a cap of magnets make me "smarter"?
Short answer
A cap of magnets, or state-of-the-art TMS protocols, will not make you smarter. 

Background
First off, TMS uses bursts of magnetic stimulation in the order of milliseconds (Rothkegel et al., 2010). Pulses of magnetic stimulation are used, because permanent magnetic fields will not induce current flow. Hence, wearing a cap of permanent magnets will not do the job.

TMS can be used using single pulses to evoke motoric muscle twitches when applied to the motor cortex, or to evoke phosphenes when applied over the visual cortex (Thut et al., 2003). In the clinic, typically repetitive TMS (rTMS) is used, where the subject is exposed to trains of TMS pulses (Horvath et al., 2010). rTMS is nowadays approved to treat depression. A popular description says it 'activates neurons' in the prefrontal cortex (ABC News), but a more realistic view is to say that nobody knows why it works, and whether it works (National Institute of Health). It's also been investigated to treat psychoses or to decrease ear ringing (tinnitus). 

Hence, TMS is generally applied to disrupt ongoing neural activity, i.e. to remove something. Indeed, TMS is typically associated with a disruption of function. For example, visual task performance is decreased when folks are subjected to TMS pulses (Thut et al., 2003). Hence TMS is not applied to add or enhance brain functions, let alone higher cognitive functions that govern intelligence.

References
- Horvath et al., J Vis Exp (2010); 45: 2345
- Rothkegel et al., Clin Neurophysiol (2010); 121(11):1915-21
- Thut et al., Clin Neurophysiol (2003); 114(11): 2071–80