I was thinking about this subject the other day, and am glad this came back up.
I have had XM for 4-5 years now, and was generally neutral about the merger in the weeks after it happened. 90% of my non-baseball time is spent between Channels 43-55, and I probably only listen an hour or so a day, on average. Mostly in my car - I forget to bring it up on the computer at work, which pisses me off when I remember.
Anyway, given my fairly narrow interests and limited listening time, I would now say I am not neutral anymore. I seem to notice a "dumbing down" of the playlists post-merger. I don't hear the variety I used to. 44 (80s alt) and 47 (current alt), two stations I listen to a lot, seem like mostly greatest hits/top hits stations now. There used to be far more variety, and a greater number of songs in the rotation. It also seems like I hear more DJ chatter now. Of course, on Deep Tracks (40), DJ chatter has always been a part of it; although chatter isn't a good description, more like mellowed-out rambling. This fits in with the sort of 1970s FM radio ambience I think they try and maintain. Of all the channels I listen to, Deep Tracks seems to have changed the least, and I am thankful for that.
But I am a little worried about the other stuff (54, the 90s alt station I also listen to, is going through a similar thing as 44 & 47.) The whole reason I got XM in the first place was that commercial radio had become unlistenable for me, with the endless commercial blocks, more and more piped-in segments, and very tight playlist rotations. If XM/Sirius continues to move in the direction I sense it is, at some point I will have to decide if the excellent MLB coverage for half the year outweighs the fact I cannot listen to the music channels anymore.
Of course, I could be imagining all this. I am curious what other subscribers think, and, if they agree with me, is this sort of thing happening up and down the dial, on the stations I don't listen to as well?