I have XM receivers in my cars (an Delphi OEM and a XpressRCi) and a Sirius receiver in the house (SCH2P) and mostly listen to Deep Tracks. The Sirius receiver started doing audio dropouts at some point between May 19th and May 20th. I know this for a fact because I record from 3am to 5am to play back later in the day when Tom Petty's Theme Time Radio Hour is on.  
It was really bad on May 20th. At 11:58am (PDT) and 4:04pm the audio was totally trashed.
Anyway, I called listener care, transferred to product support and was given a trouble ticket number and told someone would call me back in 7 days. I'm not on my third iteration of this; they have yet to call me back once and every time I call them give me excuses and tell me I'll definitely get a call back in 7 days.
My sat signal strength is 100%. And I can tell I'm not losing signal. What that happens, my A/V receiver loses lock on the toslink. But during these dropouts, the receiver is fine. In addition, I spent a few hours listening to the analog rca stereo outputs and they were glitching too.
It was starting to look like my 18 month old SCH2P was failing so I bought a new receiver last week (SRH2000). I haven't activated it (I have a lifetime on the SCH2P and am trying to avoid using up a transfer slot and paying the $75 transfer fee) but I managed to catch the end of the free broadcast that ended on the 6th and never heard any dropouts.
I've also never heard any dropouts on any of my XM receivers but I listen
to the home tuner a lot more.
I'm sure I heard at least two long (> 100ms) dropouts on Deep Tracks today. But things are a lot better than last week. The next time I hear a dropout I'll try to capture the exact time and post the details. If a couple of us do this we can tell if the problem really has been fixed or not.
 I heard Nina Blackwood call it that last month.
 Tom's show is good but not five freaking hours a week good.
I listened intently this weekend for many many hours. I head (2) audio 'skips' of about 1/4 of a second. This was at my fixed station.
The problem is definitely still there, but it has improved dramatically from where it was at a month ago. I cannot even say for certain that it would not have a periodic audio 'skip' before, but since it had gotten so bad I am now paying attention to every detail.
Problem is much better, but still not 100%.
I listened all day out in the yard yesterday . Was pretty good .
So what's the bottom line here? Is it fixed or not? I haven't noticed any problems for several days, not like it was last month. But nobody has "notified" me of any fix, or aplogized for any interruption of service. I'd like some of the last month or two back as a credit as some other posters have mentioned, but I don't want to deal with the purgatory of Sirius Customer Service. I've got two receivers on the Sirius and have been a subscriber for 6 or 7 years. I've had to activate 7 different receivers (due to cheap Xact equipment) over the years, so I know how Customer Service can be. They're fine as long as you're buying something, otherwise forget it. And Sirius has no problem contacting me by email; I get an ad, or a channel line-up or a "please come back" email every other day. They don't even know I'm still a subscriber! I agree with the earlier post; if they just would have just notified us that they were experiencing "technical problems", I could have been a lot more patient.
I haven't heard any more issues . They said they gave me a months credit , I haven't actually checked yet though.
I would call this issue resolved. Sirius over over the satellite has been rock solid for a couple of weeks now. I have not heard any of the characteristic audio dropouts/skips that were happening before.
It would be nice to know what happened, but I am sure we will never find out.
I realize this post is about a year old but I have been experiencing A LOT of skipping on my Stiletto 2 (SL2PK1) and it's driving me insane. I read most of the thread and it states they fixed the problem. Then why now, a year later, is it still happening. Was there something you guys did with your units to fix it or do I just have to call customer service?