From looking at the reviews I was a bit unsure about getting MobileMe, but after recently getting myself a iPhone 3gs and being a macbook pro user I decided I wanted to have everything in sync so I went for it.
In the small box you get your code to start your account straight away, and your live in seconds.
I think people who have had problems with data being erased should look into the settings a bit more as you can decide if data is replaced/updated etc. and you can have alerts to ask your permission if something will change a certain % of your data (useful if you accidentally delete a load of data for example).
I am very impressed with how fast everything syncs, taking no more than a few seconds, and having the email go straight to my iPhone is great.
The iDisk I found is very fast and reliable and although people have complained about the reliability of the iDisk, I think apple has now sorted it all out. Please note, the 20GB of storage is split into 10GB for iDisk, and 10GB for your email, but you can upgrade storage at additional cost.
The new 'Find my iPhone' feature is great, and I tested it the otherday to see how long it would take and only took a few moments, although this is a great feature I hope I will never have to use it!
Overall a great purchase and I would recommend it if you get sick of having to dock, and self sync.