My household has two Hoppers with Sling. My Hopper got S338 on 3/5 at 1:03 a.m. I was watching television when it took place at midnight and the entire process took an hour. For unknown reasons, the living room Hopper missed the update for two days but it finally updated 3/8 at 1:10 a.m.
The first change I noticed immediately (after the promo for channel 100 being added to the screensaver when the unit is powered down) is when you view TV Activity, the text size of Tuner 1, Tuner 2, and Tuner 3 is huge and there is no longer a space dividing the header (Ex: Watch Live - 3 of 3 Tuners in Use) and the Tuner list.
The next change I soon discovered was that the number of timers has been increased. The timers could never go over 96 events. Suddenly I found myself able to pile on the timers. I reached 200 before it informed me that I had reached the maximum allowed! I told advanced tech support about this hoping to get a confirmation of the added feature but they insist that the maximum has not changed and is still 96 timers.
Also I would like to address the issue of the Hopper wanting to update. Without fail the intrusive update pops up at 1:30 a.m. and this concerned me as well since I almost always have a show recording at this time. Obviously, I don't have any desire to have the Hopper disrupt my recording so I tell it 'no'. Then the Hopper will next ask around 2 a.m., if you tell it 'no' again the next time it will prompt you at 2:30, and so on all the way until 5:30 a.m. if you never allow it to update. Of course I was upset thinking any early a.m. recordings could be interrupted while I was away or not paying attention. I was in disbelief since before the Hopper always had the courtesy to wait until there was inactivity before requesting an update. For two days I thought I had to "babysit" my Hopper while I recorded during those key hours when it would want to update, and out of frustration I finally mentioned it to tech support. Most of them agreed with me but one person the other night actually told me that it's a new feature. Unlike with S335, apparently S338 no longer requires a complete shut down and reset to perform an update. He explained that the update can take place if you have at least one free tuner and it will not disrupt your recording. In a way this makes sense because it would explain why the Hopper has suddenly become so persistent to update no matter if I have a recording going or not. I am positive that there are lot of upset people assuming as I did that if I allowed the update it would reset and lose my recording. What it actually does now is just puts up the screensaver as if in standby mode. The recording isn't affected.
I am hoping that the S338 update improved the stability of the Hopper. I was at the point where both my Hoppers were experiencing constant STB Reboots. It was triggered by such basic actions as deleting a timer or creating a timer or even viewing a show's program info. This resulted in anything that was recording being split into three halves. The first half was the bulk of the show, the second half was 0 minutes, and then the third is after it resumes the recording after the reset.
Some recordings still randomly display as 100% watched so that bug hasn't been addressed yet. I have encountered several other detrimental quirks as well in the short time I have had S338 such as a recording taking place but with it x'ed out in the guide as if it has been cancelled and no red receiver light during. I've had several timers get stuck "About to begin recording" in the TV Activity menu but never actually recording. I've also had timer events which were skipped "due to conflict" suddenly come to life in the Daily Schedule and light up as red as if recording, but of course there's nothing being recorded. However, if you reset the receiver, when it comes back the show will now be recording and has to be manually stopped.
Another lovely side effect seems to be corrupted recordings. I define corrupted as when I go to play back the show or movie and it gives me a pop up message as if I have just finished viewing it and have reached the end. The hours are there and the size is there but the recording is lost with no way to actually get it to start. Both Hoppers were affected and it ruined a few Showtime and The Movie Channel movies but specifically targeted and obliterated everything recorded on the networks Syfy and Chiller, it didn't matter whether it had been stored on the Hoppers for months or if it was just recorded over the last few days. Other movies and shows on STARZ, EPiX, IFC, AMC, FX, TNT etc. appear to be fine and safe.