It seems that every thrity-seconds of playtime, the game freezes for a short duration. Even the main menu and steam menu freezes! This happened ever since the 1.5 patch was installed. I uninstalled all my mods and this is still happening. It's really starting to get annoying, especially in the middle of combat.

specs:
Nvidia GTX 285 1GB
Intel i7 920 2.6 Ghz
6 GB of RAM
Windows 7 Ultimate

what are your save game size, i noticed that when save games start to bloat, this is exactly what happens.

Between 200,000 KB and 100,000 KB.

Out of curiosity have you timed these freezes, or are the 30sec you refer to an estimate?
I ask, because this issue started for me out of the blue as well. I timed them to occur almost every 70sec. A 5sec freeze followed by another 70sec of interrupted gameplay 5sec freeze etc etc. The cycle repeats almost to the "t".
I've spent the past 2weeks troubleshooting to no avail. I was certain it was early signs of a hardware failure, but found this problem did not exist in any other games.
currently in process of reinstalling skyrim and all my mods. I've seen many posts about lags freezes and crashes but nine specific to mine until I just read your post.

I didn't time them, actually. I just estimated that it was probably between 30-whatever seconds. I just happens out of nowhere. It isn't some RAM or texture problem, it seems. I thought that it were mods deactivating and activating by conflicting issues, but I don't know.

So far through my troubleshooting steps: aside from the countless measures I've taken outside the game environment, after rein stalling skyrim and all of my previously installed mods with 1.5.24 (1 release ago I believe) I managed to start a new game and played about 20min without experiencing the same freeze. (At this point all saves prior to reinstall had been moved to backup drive)
I then placed my latest save (prior to this reinstall step) back into my save directory. (That save is about 67,000KB)
It loaded fine, but sure enough 70sec in, the freezes began once more.

This, IMO, narrows this down to one of two things. You mentioned these freezes began for you right after updating to 1.5. I could not recall if that was the case for me or not. So....
Its either,
1) bloated save file, or
2) the 1.5 update
Im calling it a night so ill resume my steps tomorrow with
Backing to previous 1.5 (whatever update that is, I know I have backups)
->if that fails to be the case then I'd say it stands to reason the bloated save files are culprit. If so, I don't know if any current measures are in place to circumvent without beginning a new game. Which svcks, because I'm still on my original playthrough, and I explore every inch and do any and every quest possible. And at 500+hrs, that's more than I'd prefer to start over.
Regardless, any additional input or results on your end are more than welcome

I started a second game just recently because I was getting bored of my spellsword. I've yet to beat the main quest, the theives guild, or the mages guild yet.

I'll start a new game for great justice, and see if anything bad or good happens. Thanks for your help, man.

Hey mate, just to clarify when you say Between 200,000 KB and 100,000 KB.

You are actually saying between 100 and 200 megabytes? In which case your save files are very bloated.

Try this

remove all your mods, delete DATA folder, use steam to recheck / redownload the files so your back to vanilla.

Then wait 31 days in game and see if the next save file is smaller,

I have also done this and the bloating becomes less but is still there with 1.5.26.

Okay guys, I started a new game and everything is back to normal. I guess the saves were bloated after all.

I don't mind restarting, anyways. Thanks, folks.

Your seeing the same results as I am then. If anything's, it just further reinforces.
I'm still exhausting all efforts to salvage as much of my previous playthrough as possible, n still seeking a method reduce the size of the bloated files. I even started a thread in an attempt to collect data from everyone experiencing the same issues,but so far no one is taking to it. Maybe in time. My only suggestion moving forward would be to keep a close eye on you save file sizes and stop the bloat in advance in the event it starts once more. Good luck

Are you using waaay too many High Res or HD texture packs? this is exactly what happends when your GPU runs out of memory.