Question: I read the related answer to whether photons have size, and the answer seemed to be it depends. If a Photon, or a rather an E&M wave has a magnetic and electric field, should things be able to feel this? I know electrons do get 'sloshed' in these fields, but what is the range of influence of a photon? How much space do the waves physically occupy?

Answer: 
Perhaps a good way of thinking about it is that a photon is produced by some process: a free-space decay of an atom in free space, to a stimulated emission in a laser cavity, etc. These processes have a spread in energy(frequency) known as their bandwidth. Since frequency and time are conjugate variables in QM, the temporal length of the photon is constrained by the Fourier transform of the bandwidth, and since we know the propagation velocity of the photon, this defines it's length. The transverse dimension of the photon is given by the mode of the resonator that produced it (the dipole pattern of the atom, or the Hermite-Gauss mode of the laser cavity).

As an example, consider an atom in a laser cavity which has a mode waist of 1mm, and a bandwidth of 1 MHz (assume that the natural line width of the laser is much larger to keep it simple). The photon emitted from the cavity would be distributed along a volume which is transversely 1mm in diameter and longitudinally is c/1MHz ~ 300m long. As mentioned above, one typically views this as the probability envelope of a the photon so that over many identical realizations of the single photon event, one would find the above probability distribution in space or time.

From the standpoint of pure quantum optics, one formally considers a resonator in which the E-M field is a standing wave and has a lowest energy ground state. From here you find that the Hamiltonian is that of a harmonic oscillator and has single excitation (Fock) states which represent single photon. To think of photons in free space, one typically extends the dimensions of the resonator to infinity. This allows you to sleep better at night because it's rigorous, but I find viewing photons as described above more useful for understanding physics.
At very low energy, the difference between photons and E&M waves becomes clearer: After every spin-flip in a hydrogen atom, "something" with E=6 µeV and spin=h/(2\*pi) is released. Is that "something" a photon? Nobody can detect a photon with such a low energy. But if you have a radio receiver at 1420 MHz, you get a clear signal. The electric component of the wave accelerates electrons in a wire called dipole antenna and you can measure a weak current. Where is a photon? Radio receivers do not detect photons!

If the atom releases a photon, something transforms it to a long wave packet. Where? Is the intermediate photon necessary? Perhaps the atom emits the wave packet. How? Nobody knows.

The optimal length of the dipole (0.1 m in this case) corresponds to the diameter of the wave packet: a shorter dipole provides a weaker signal, a longer dipole brings no additional gain.

The coherence length of this wave packet is about 60,000 m. You can calculate using the FWHM = 5 kHz, measured in astrophysics. This huge wave packet is a big contrast to a point-like photon.