My Magus has extensively used Art of Memory (at an ability of 7), as well as having the spells Enhance the Memory Palace, Memory Palace of the Sage, Constructing the Memory Laboratory (of course customized to suit him), and a custom version of Constructing the Memory Palace (Level 25, T: Group to create 10 rooms and Size 1 to create 10 Loci in each room, so 100 Loci per casting).
His "Memory Palace" consist of six large rooms of a Mediterranean style villa built around a courtyard in a hexagon array, with each room having a pedestal in each corner and one in the center of the room (5 per room, this is natural from his skill). The central courtyard does have 5 Loci, but it is also the location of a large fountain (where short term memories from Enhance the Memory Palace are stored) and has stairs up and down. Going up the stairs leads to a small comfortable library which currently has eight books (from Memory Palace of the Sage). Going down the stairs leads to a basement with ten small rooms, each with a scroll rack and reading lectern (Constructing the Memory Palace).
A pathway leading from the "Memory Palace" leads into a massive hedge maze made from rosebushes with gemstone blooms. In the center of the hedge maze is his "Mental Lab", constructed as a more whimsical version of his normal lab. All of the lab tools and equipment fly about and respond to command, assisted by a hoard of magical flying hands. The light and temperature are always perfect, adjusting to precise command. Located under the "Mental Lab" is another basement of ten small rooms each with a scroll rack and lectern (another Constructing the Memory Palace).
His uses of them are varied based on the locations they make up.
The 35 Loci in the villa are the ones he uses for common things, the ones most likely to be willingly forgotten. Names (and descriptions if not that many) of all the Magi who will be present at a location, maps for areas he will be traveling through, important conversions he witnesses or takes part in, Tribunal notes (Magi position on an issue and vote), important notes gained from research on a short term (which could be many years for a Magus) project, and so forth. Any worth keeping are written out or moved to the basement, with them being erased as necessary for space.
However one of the Loci in the Courtyard is special, in that it is his mother as she appeared the last time he saw her alive. It has her look, feel, smell, and sound (from that last conversation). She serves as the "library index" for the memory palace and he will also spend time talking with her (which is actually talking with himself) when trying to figure something out.
(Edit: Forgot the Library)
The books in his library are a mix of things he wanted to study while traveling and reference books. One of them is "De Theoria Magica" by Bonisagus, which is considered the Authority on Magic Theory (and thus useful since most Commentary on Magic Theory are based off it). He also has "Of the Magic of the Human Form" by Oberr of Verdidius (Summa on Corpus, L 26, Q 5) which he still studies a little from during long travels. Rounding it out are two Language (Ancient Greek and Demotic Egyptian) and three Area Lore (Canaan, North Atlantic, and Mythic Europe) Summa.
The 100 Magic Loci in the basement under his Memory Palace are mostly used for "long term" storage of things which he might need.
One of the rooms is focused specifically on his Covenant, containing such things as a census of the Covenant (all non-turb, with basic info), Turb roster (as census, but more detailed), index of the Library (Books with Author and Subject), Enchantments & Rituals list (Covenant owned Enchanted Items, yearly rituals, etc), Covenant Holdings (Land, Workshops, etc), Covenant Treasury (the "Books" as if it was a business), Magi Secrets (commands for Magi only items, along with other information), and Notes (just general things he wants to remember). He has two free Loci in the room.
Another room is dedicated to the Landen Mystery Cult, currently storing seven Mystery Scripts.
The other basements rooms include things like Tribunal Notes, Important Conversations, Maps (of locations commonly traveled to), etc. Anything that he needs to remember on a regular basis or might be important years later.
The 100 Magic Loci under his "Memory Lab" are used for Lab Text and Lab Notes. Our group ruled that the low annual cost (it is 0.05 pounds per season) of a Mental Lab was for the paper and ink to take Lab Text/Notes, which are not free. We did classify them as small enough to fit within a Loci however, thus this dedicated space.
Play wise, it allows him access to any researched information, maps, and the ability to ask the SG to repeat anything he classifies as important in play (ie tells the SG "memorizing"). People he interacts with he mostly knows their name, job, and important trivia about. He is by far the most popular Magi among the Covenfolk who does not have the Gentle Gift.