Apparently there are no strings are attached in this big free giveaway. You will just need to wait for their website to recover from the crash due to the massive traffic to download the Creative Suite. Creative Suite 2 “CS2” contains Photoshop, Illustrator, and nDesign. I am not sure Adobe did this just to be giving and charitable in the new year but perhaps down the road convert a percentage of those that download to upgrade or buy a new products.
UPDATE: Gizmodo and multiple other major tech media apparently have got it wrong, as well as customers were sent the notice to download serials and software free because they (Adobe) were shutting down their CS2 activation servers. It is embarrassing for everyone, especially Adobe who will need to write more clear notices in the future. I would not like to be in their PR group today.

http://blogs.adobe.com/conversations/2013/01/update-on-cs2-and-acrobat-7-activation-servers.html

Check out Gizmodo’s article:

Grab Photoshop and CS2 For Absolutely Free, Right Now

And theVerge

Adobe's Creative Suite 2 now available free of charge for older PCs and Macs

Accurate News:
If you want a great alternative to Photoshop that has many advanced features, does not require a monster download, or take tons of disk space check out Autodesk’s free web based Pixlr. Pixlr is the worlds most popular online photo editor and also has mobile apps for iOS and Android.

Cheers,
Shaan