Our is locked....but the back is completely open as it had to be removed to fit our new MIS server in. Hoping to get a new rack and tidy the gaff up this summer.
Working along the lines of the H&S principles Tony mentions, this is how we plan racks at Luton Six Form College:
UPS (not that we have any in rack in server rooms these days) at the bottom of the cab - H&S dictates keeping the amount of lifting needed to get these beasts into place to a minimum, not to mention avoiding making the rack top-heavy.
SANs tend to go just above these lower level things, again avoiding putting very heavy stuff higher up than needed. We don't put these right at the bottom of the cab tho due to advice from Dell/Unisys who pointed out that disk enclosures pull a lot of air in and if they're at the bottom of the cab this will include a lot of dust.
Switches - if they're network infrastructure, then in a network infrastructure cabinet. If they're part of something else (e.g. phone system, iSCSI) then with the item they support. That's how we do it anyway, if you can't have a separate switch cab then I'd suggest near the top, keeping in mind access to them needs to be as easy as possible. Don't forget that its possible to mount switches on the reverse side of a cabinet, which works well for SAN fabric switches, for example.
KVM monitor/keyboard tray (if applicable) - roughly in the middle at a comfortable height for operators. These are actually the first thing we plan/place due to operator comfort/H&S being paramount.
Tape Autoloaders or anything else that requires frequent operator access/intervention as part of its normal operation: roughly in the middle at a comfortable height for operators... which translates to directly just above or just below the KVM tray.
One of the other things to consider is airflow within the cabinet. I tend to put this under H&S as it is to do with performance in a given environment. Some kit now comes with different airflow compared to previous kit ... the newer Cisco routers with side to side airflow is a pain in the next for some folk ... so it might need to be in a different rack (are per @Roberto's comment on comms infrastructure being in its own rack).
This is the setup of one of our typical site cabs, the server suite cabs are different.
In ours UPS's go at the bottom, then servers, followed by routers and firewall, then patch panels and switches, spaced out at 3/4 panels then switch. at the top is a distribution switch and any fibre. Depending on the cab at the back at the top will be fibre and any phone lines that come in and terminate to a patch panel.
We have 4 different cabinets. Two Cabinets used for servers (each less than half-filled). One Cabinet used soley for storage/iscsi switches and one Cabinet used for Comms Equipment. This way everything is pretty much kept seperate and with any cabling that gets done I don't have to worry much about the servers. We have a seperate floor standing UPS (some 3 phase beast) that goes into a seperate power distrubition unit to feed each cabinet. We have the server room on a seperate lock, each cabinet is locked and all the servers/storage units etc where they have lockable bezels also have these locked too.
On the server cabinets switches are kept at the top, but mounted on the rear rails - largest/heavyist servers (4U) at the bottom - working the way up to 1U servers. On the comms cabinet - patch panels at the top, then the core switch/router and below that firewall, ruckus zone director etc.
Roberto I wouldn't mind taking a look around. I have heard good things about your place :-)
Perhaps a Beds IT Tech meet up? :-)
Thanks all for your suggestions. We managed to get everything installed yesterday and all looks pretty good. Just ordered a rang mountable KVM with built in tray with monitor etc, will will finish the job off nicely. Then time to get comissionining.