I have been using Gladinet for approximately 3 years. I
started with the basic free edition and moved on to the Pro, fully paid
edition.

It is used primarily for documents and the odd large business
presentation. No pictures, movies, or anything more than 5mb.

Whilst it works fine for smaller files (less than 1mb), the
software is severely restricted for files over 1mb. It downloads them two or
three times before it manages to open them, it is abysmally slow ( one or two
minutes to opening), and sometimes it simply does not open them at all.
Numerous email exchanges with the support team later, having gone through
debates on internet speed, firewall connections, settings, etc, etc, and having
found out they were all ok, the concluding remark is “uninstall and reinstall”!!!
Even so, problems persist. The software is basically good but is not designed
to handle large files.

In summary, if you have small files and want quick access
via a “drive”, it works. But do not expect to manage a large file portfolio via
gladinet. You will simply end up back using the web portal like you always did
before gladinet… 

Regarding Amazon S3, personally I don't believe it is that expensive at all (http://aws.amazon.com/s3/faqs/#How_much_does_Am…) but all providers have their charges out there for comparison, so it is a choice.

SMEStorage lets you view all your files in one virtual file system(http://farm3.static.flickr.com/2656/4004691124_13bf163874_o.png) and also supports cloud import /export from different cloud providers, including additional support for Google Docs and Evernote(http://farm3.static.flickr.com/2528/3817602348_fb43148f27_o.jpg).

Additional services are Email Backup, File sharing (via url, Twitter, email and RSS) integration with Zoho Office and Picnik, collaboration features, and workflow rules.