I'm running this on Mountain Lion 10.8 and so far it is running smoothly. iStat Menus has become a must have, cannot live without app. Pure awesomeness.

Its a replacement for all build-in sensors battery/CPU/Fan plus clock/calendar
an absolute must have for every MAC user!

So far so good - hasn't tanked my system yet like the last update...

I tried several stats apps, and this one was the most reliable, most flexible, and has the best UI for my purposes. I keep just a few of the widgets in my menu bar, and having RAM, CPU and temp at a glance up there, in simple, unobtrusive colors, is very helpful.

I have tried a lot of various system monitoring utilities, and iStatsMenus was a pleasant surprise. There are a lot of little touches that make this a "must have" monitoring utility for system monitoring geeks.

It gives a lot of information display options and has high level of configurability. Being able to "bundle" many system monitors under one menubar item (MBI) is invaluable on a 13" screen. The network activity has replaced MenuMeters', but the CPU from MenuMeters is better, and still on my menu bar.

Being able to change the battery from percentage to display dynamically depending on if it is on AC adapter, on Battery Power or Fully Charged is probably my favorite "little" thing because it is so valuable in actual use.

Having the monitors almost completely customizable has replaced about 4 or 5 other monitoring utilities and stock menubar items. I removed my temperature monitoring app, the default date/time, a 3rd party Date/Time MBI, MenuMeters Network monitor, in addition to the stock Battery MBI.

A few "touches" such as showing the moon phase and your public and private IPs (IPv4 & IPv6) are bonuses. The public & private IP under the network pulldown is actually very handy.

But I'm only giving it 4.5 stars because it could be improved in the following ways (all total "pipe dreams" at this point):
Aside from a better CPU MBI, I wish I could "bundle" fantastical's features as well, but I know that's a tall order.

But I think the developer could replace the Airport/Network display icon and time connected display by allowing it to be rolled into the Network display (I would allow a color-coded wifi signal strength to be over-layed or under-layed behind the graph or whatever display a person chose). I would also allow the gateway to be seen, the Network Diagnostics "lights". Also the calendar icon with the month would has a color on top option. I would "link" the color code to event in iCal. the default color codes would use ROYGBIV "red" = "within 1 hour" and fade to "violet" for things a week or two out. White or Black digits could signal an empty calendar for the night. I'd default to white text on black for "no more upcoming events for either til the next day or within the next 12 hours.

Overall I say try it and buy it if you like it as much as I do. I was lucky that I got this in a MUPromo Bundle or else I would never have discovered it.

i installed a new HD on my 27" iMac since it died after only a 18 months. swapping out new HDs on the new iMacs causes the HD fan to constantly spin up to 6000rpm since Apple has a propriatary temperature sensor on the HD which is not compatible with other HDs.

i am very disappointed that iStat Menu doesn't work with controlling the HD temperature. of interest, the other 2 fans are controllable just not the one that originally drew me to downloading the application in the first place.

the only application that actually works is HDD Fan Control, but at $30 that application is a bit of a rip off. i would gladly pay $16 for all the features that iStat Menu offers if only it would control my HD fan!

I just bought iStat Munus and the current version seems to have a bug where my GPU memory usage never changes. I don't recall this bug with version 3.16

Does anyone know what the new "Combined" menu extra does? The dev's website/Online Help says almost nothing about it, nor does this MacUpdate.com post.

It's quite bugged on my computer : the speed fans control which is very interesting for me doesn't work properly... I'm going to reload and reinstall the app to see if there's a change otherwise I won't buy it.

Bug in v2.0 (OSX.5.8, G4): Whenever I connect to the internet, all AppleMenuItems are restarted (they disappear, then reappear) which often takes up to 60 seconds (annoying) and does not happen without iStatMenus. Please fix it...