Spotfire Silver version 2.0 is available now on https://silverspotfire.tibco.com/us/home and it will be officially announced at TIBCO User Conference 2011 (9/27-9/29/11) at http://tucon.tibco.com/
Spotfire Silver available in 4 Editions, see Product Comparison Chart here: https://silverspotfire.tibco.com/us/product-comparison-chart and Feature List at Feature Matrix here: https://silverspotfire.tibco.com/us/get-spotfire/feature-matrix
Update 9/27/11: TIBCO officially released Silver 2.0, see http://www.marketwatch.com/story/tibco-unveils-silver-spotfire-20-to-meet-growing-demand-for-easy-to-use-cloud-based-analytics-solutions-2011-09-27 "TIBCO Silver Spotfire 2.0 gives users the ability to embed live dashboards into their social media applications, including business blogs, online articles, tweets, and live feeds, all without complex development or corporate IT resources... Overall, the software's capabilities foster collaboration, which allows users to showcase and exchange ideas and insights -- either internally or publicly. In addition, it allows users to share solutions and application templates with customers, prospects, and other members of the community."
Spotfire Silver Personal Edition is Free (Trial for one year, can be "renewed" with other email address for free) and allows 50MB (exactly the same amount as Tableau Public) and allows 10 concurrent read-only web users of your content. If you wish more then Personal Edition you can buy Personal Plus ($99/year) or Publisher ($99/month or $1000/year) or Analyst ($399/month) Account.
In any case you will GET for your Account needs a real Spotfire Desktop Client and worry-free and hassle-free web hosting (by TIBCO) of your Data Visualization applications - you do not need to buy any hardware, software or services for web hosting, it is all part of your Spotfire Silver account.
To test Spotfire Silver 2.0 Personal Edition I took Adventure Works dataset from Microsoft (60398 rows, which is 6 times more than Spotfire's own estimate of 10000 rows for 50MB Web storage). Adventure Works dataset requires 42MB as Excel XLS file (or 16M as XLSX with data compression) and only 5.6MB as Spotfire DXP file (Tableau file took approximately the same disk space, because both Spotfire and Tableau are doing a good data compression job). This 5.6MB size of DXP file for Adventure Works is just 11% of web storage allowed by Spotfire (50MB for Personal Edition) to each user of free Spotfire Silver 2.0 Personal Edition.
Spotfire Silver 2.0 is a very good and mature Data Visualization product with excellent Web Client, with Desktop Client development tool and with tutorials online here: https://silverspotfire.tibco.com/us/tutorials . Functionally (and Data Visualization-wise) Spotfire Silver 2.0 has more to offer then Tableau Public. However Tableau Public account will not expire after 1 year of "trial" and will not restrict number of simultaneous users to 10.
Spotfire Silver 2.0 Publisher and Analyst Accounts can compete successfully with Tableau Digital and they have much clear licensing then Tableau Digital (see http://www.tableausoftware.com/products/digital#top-10-features-of-tableau-digital ), which is based on number of "impressions" and can be confusing and more expensive then Spotfire Silver Analyst Edition.