Chris McNamara, www.supertopo.com writes:

The Muir Wall is one of the few really classic moderate routes on El Cap that does not receive tons of traffic.
Then how difficult is it? Most of the pitches are C1 and C2. At its hardest, it is about as difficult as Zodiac (A2). But the main challenge of the Muir is its length. Also, because there are few pitches rated 5.7-5.9, almost everything must be aided, which is time consuming.
Since the Muir Wall is soo long, it is reccomended for teams that can move fast.
(Reprinted with permission)

The climb we did back in 92, which is also the one described in this article, was a mix of the Muir and Magic Mushroom. Up until pitch 13 we were undecided which of the two to do. We started to fix on the Mushroom, did 5 pitches and realized there was no reliable anchor possibilities to get back down without swinging over in the Muir. This one we followed a short stretch before getting back to the Mushroom. In essence we climbed almost the entire lower section of the Magic Mushroom, all excellent, memorable stuff, before finally committing to the Muir after Mammoth Terraces. This is well explained on the topo.
It is possible to avoid all this lower confusion via Salathe's Free Blast. Bad idea.
We had done the Free Blast before and knew it wasn't the best section of climbing on El Cap, besides the fact that it's a free climb, as the name implies, and the Muir et al is an aid wall (or was). Better to get in that groove from the beginning and do the seldom visited lower pitches below Mammoth Terraces. Expect that it will add a day to the climb, but that's what it's all about: Hanging out on the wall.

For us it was an aid wall almost exclusively. We found short stretches of free climbing thru out, but very little of it was hard, of particular interest, or scary. The exception might be most of pitch 10 and the steep crack on 13. The former was a smooth runnel with a seam in the back, blown out by repeated nailing. Pro was sketchy, the balance quite awkward and everything about it felt insecure. This feeling changed very little when finally I started aiding.
As on most El Cap routes in this area from the Nose westward, the first dozen or so pitches are relatively low angled. The features are more indistinct, the cracks are sometimes bottoming and things can get almost slabby. At Mammoth Terraces the wall rears up, and stays at or beyond dead vertical for the rest of the route. The cracks and corners up here gets sharp edged and long, with well defined features such as the immense dihedral on pitches 27 to 31. The Muir doesn't have any huge roofs (like below the Headwall on Salathe) nor does it have the constant 110 degree inclination of the South East Face. Just thousands of feet of really steep climbing.
Aiding on the Muir was in the classic idiom. Lots of straight forward A1 and A2 cracks, the majority of which were clean and absolutely beautiful. Very few hooks moves, only a few feet of copperheads. The cruxes were, as it always seems to be on older routes, creative installations in shallow, blown out pinscars. This said, there certainly were some very pristine appearing thin cracks too, that took the tinyest nuts and KB's. These sections we found mostly on the desolate, seldom gone lower pitches.
All in all the climbing is not desperate, hardly scary and certainly not dangerous. It is a mellow choice for a seasoned aid climber, but a perfect and most enjoyable outing for someone relishing in sustained, esthetic and strenuous aiding on flint hard and flawless granite (thanks to Largo for coining that last phrase).

In 1992 we had no Cam Hooks. All the rest of the clean aid arsenal was essentially the same back then as it is today: Aliens, Hb Off Sets, Bird Beaks etc. But with those Cam Hooks, Ed Leeper effectively removed the need to pound in hundreds of pitons on the old classic El Cap routes. Even average aid climbers like us could have gone clean with ease, where we frantically groped for the pin rack and slammed in dozens of LA's or wacky sawed offs.

But anyway, here's the list of what we brought, without updates (remember this pertain only to the Magic Mushroom/Muir hybrid described here):

2 sets of HB Off Set brass nuts
1 set of HB Off Set regular nuts
1 set of RP's
3 sets of Rocks
3 sets of TCU's
4 ea #1 - 1.5 Friends
3 ea #2 - 4 Friends
2 ea #4 Camalots
4 KB's
12 LA's
15 ass. angles, inc. 1 - 1.5"
10 copperheads
all hooks
10 rivet hangers
80 biners
lots of runners

Notes to gear: Some of the cracks are very long, parallel sided and consistently 1 -1.5" wide. Very much like an Indian Creek splitter. Bring cams accordingly, to avoid some of the hefty back cleaning scenarios we encountered.
Since the much talked about free attempt involving illegal power tools, you must assume the anchors have been beefed up a bit. This would be nice, since I remember more than one instance of dangling from a handful of beat up 1/4" bolts with copperheads leading to and fro the belay.
To the best of my memory, there's little or no need for cams larger than a #4 Camalot. We didn't own anything bigger, save a #3 Big Bro which was left in the car. That said, it is prudent to include a few bigger units so you always can aid yourself out of some heinous OW horror.

It is off course unlikely you'll end up at the same bivvy locations as we did, but here's the beta about ours (all were spent in port-a-ledges):

First night: Top of pitch 11. Not tremendously exposed. Good smallish ledge to get organized on. Excellent anchors. Fine spot.

Second night: Top of pitch 18. Very exposed location under the Shield Roof. Many parties pass by here, so the anchors are in good shape, but you might find someone already hanging from them. (Those scandinavian readers with NTK's 1983 Anniversary Edition on their shelves, will find an excellent shot of this bivvy on p. 77.)

Third night: Top of pitch 24. In the middle of an amazing stretch of soaring corners and killer climbing sits this little triangular slab. The sudden lower angle and plentitude of gear makes for a no brainer bivvy spot.

Fourth night: Top of pitch 30. If you at all can time it to stop here, do it. The exposure is intense, the surroundings are as grand as anywhere on the route, and few obvious spots appear in the last 3 pitches. As a matter of fact the next section is one of the cruxes.