iDisk, therefore I am
A standard MobileMe account includes 20GB of server space, shared between emails, photo galleries, iWeb sites and your iDisk, which provides general purpose storage. For comparison, a free Google Mail account provides over 2.5GB.
Third-party storage and file transfer services offer more: Dropbox, for example, gives you 50GB with its Pro 50 option, but you have to pay about the same as MobileMe just for this one service.
iDisk is superbly easy to use. On your Mac it's constantly available in Finder, and you can drag files in and out, search it or do anything else you'd do with a hard disk, despite the fact that it's 'in the cloud', on Apple's servers.
Your iDisk's Public folder can be freely accessible or password protected, so you share files with other users or invite them to drop files in.
Like every other aspect of MobileMe, your iDisk is also accessible via www.me.com, where you can select any file and click Share File to email someone a link to it. The web interface lacks features such as search, which is annoying if you actually have to access your iDisk via a browser. But you don't.
Even on a PC (whether running Windows XP or Vista), you can go to Computer, click Map Network Drive in the toolbar, set Folder to http://idisk.me.com/membername, click Connect using a different user name, and enter your MobileMe name and password. Et voilà, your iDisk is accessible like a hard drive.
Similarly, on a Mac without MobileMe set up, just go to Connect to Server (press Cmd+K in Finder) and enter http://public.me.com/membername.
Back to My Mac is another feature that ensures you can get to the data you need. It gives you full control of your own Mac (as long as it's switched on) from another over the internet. This works well, but both Macs have to be running Leopard and you may have problems with some firewalls or routers – our ageing but otherwise serviceable Belkin 802.11g couldn't handle it – so it may not be as useful as it looks. Alternatives such as LogMeIn are less seamless and/or cost money.
Lost and found
Find My iPhone shows your iPhone's location on a GPS map and optionally transmits a message to it while playing a loud sound for two minutes. That will be a more reliable way of discovering where you put your phone than the traditional routine of dialling your own number, running around the house listening for the ring until it goes to voicemail, hanging up and redialling!
If you really have lost your iPhone and there's stuff on it that you don't want others to see, you can also use Remote Wipe to delete everything on it – knowing that if you do get it back, most if not all of your data can be reinstated by re-syncing to MobileMe and iTunes. Not something everyone will use every day, but reassuring.
ALWAYS CONNECTED: You can forget juggling contacts when everything's synced between the Apple tools on your Mac(s) and iPhone or iPod touch
For non-iPhone users If you don't have an iPhone or touch, MobileMe is still useful for syncing email, contacts, calendars and other data between multiple Macs and any PCs. Among the extra bits and bobs you can choose to sync are bookmarks (in Safari on both Mac and PC or Internet Explorer in Windows), Dock items and various application and system preferences.
Using a conventional POP email account means either getting email only on one of your machines or struggling to avoid ending up with your messages divided among several. If that's the way you've been working, MobileMe's IMAP-based mail, where each machine accesses the same data from Apple's server, is a revelation.
You can still keep a copy of all your mail on your hard disk. In Apple's Mail app, this is set in Mail > Preferences > Accounts > MobileMe > Advanced > Keep copies of messages for offline viewing. You can get most of MobileMe's functionality with third-party tools, but not all come with a single solution or the same simplicity.
Google's mail and web services are comprehensive, and offer more functionality if you have to use a web browser for access, but feel a bit messy and fiddly. It's also worth bearing in mind that MobileMe comes with free 24-hour live chat support. We tried this on a weekday and a Sunday, and got quick, polite and correct answers.
For most people with a second Mac (or PC) and/or an iPhone or iPod touch, the combination of unique features, decent amounts of storage, effective sync and push, and consistent presentation between devices makes MobileMe worth the outlay. That doesn't mean, Apple, that we wouldn't like to see it get a bit cheaper.