I'm fairly new to SF4, but I've run into a ton of people cheesing the hell out of Guile by spamming Sonic Boom already. How would I go about combating this?

Who is your main? Depends on who you are using, there is no universal strategy.

I've generally been playing Sagat and Hakan. Leaning more towards Sagat as Hakan doesn't seem to be very friendly for new players.

Well with Sagat, fight fire with fire. Your tiger shot is tops in the game, spam that shit. Slowly inch your way forward using either focus attacks or short tiger knees. You will need to learn footsies with Sagat, the common downfall for online Sagat's is that they have absloutely no understanding of footsies, meaning when you get close to him or he approaches you, you are lost. Pressure him with strings like crouching short crouching short tiger shot/short tiger knee. If he jumps at you, that is a free tiger uppercut.
 
I am not expert with Sagat, you not knowing what to do comes with the territory of being new. You will learn the more you play, or I should say, the more you get your ass kicked. We have all been there.

"It is a punishing game, but a ton of fun to play feels like I learn something new every match. "

Yeah with Sagat spam tiger shots and get closer.  Jump in little by little- if you sense that the Guile will do a Flash Kick, block the kick and use this time to punish him- either by throwing his ass, pulling an ultra, or do an uppercut while he is in the air.

" @Stang: And how, out of 12 matches tonight I managed to get one win. It is a punishing game, but a ton of fun to play feels like I learn something new every match. "

Guile cannot win a straight up fireball war with Sagat, so keep shooting those tigers and he will be forced to come at you. Be wary when Guile is between half screen and sweep range from you as he can follow up his jab SB with a Backfist or jump in to punish your fireball, so be patient at this range and keep him out with TK, TU, and well spaced normals. Be careful when fighting Guile close up with Sagat as Guiles close range normals outclass Sagats (don't spam sweep).

If you're new please direct questions like these to the beginniners thread, just to keep things tidy.