When I began doing my research I recall running across some negative info regarding Mozy, but I may not be remembering correctly... I think it was on a couple of photographer forums. Try Googling Mozy combined with the words "review" or "problems" etc. and see what turns up... Right off the bat I found
this blog comment about how the Mozy software slowed one Windoze computer to a crawl. I have no idea whether a Mac might experience a similar problem.
Here is another blog entry generally refuting a bad review of Mozy, but the interesting info can be found by reading the comments below the article. And
Ars Technica reviewed Mozy and three other online data storage services. The reviewer placed Mozy at the top of the four services when the review was written in July 2007. Be sure to check out the reader comments by clicking the "discuss" button at the end of the article.
One problem that I have run into is that typical upload data transfer speeds are sooooo slooooow that it can literally take days to upload a significant amount of data, so you have to ask yourself how far you want to got toward that "unlimited" data amount.
For example, I uploaded a little over 30MB of data to iDrive a couple of days ago and it took around five minutes using my Charter broadband connection. Downloading the same amount took seconds to accomplish.
Features to look for are the ability to resume an upload where it left off if the data transfer is interrupted and software that allows for incremental backups once you have your initial data upload completed. That way only the files that have been changed and new files are uploaded, saving time and server space.