If you've got CS1 and have not yet upgraded to CS2 and are now ready to goto CS3 - there's a sweeeeet deal out there that will save you some cash.
You can order the upgrade straight to CS3 and pay however much for it.
You can also still order the upgrade to CS2 and you'll pay about 40% less for this upgrade.
.... and guess what. That CS2 upgrade qualifies you for what they call a "Post Announce Upgrade" which I totally don't understand how or why - but basically, if you buy CS2 after they've announced CS3 (that would be now), once it arrives you can call Adobe and they will send you.... for free (you pay shipping) the upgrade to CS3.
Yep. I didn't mis-speak there. I guess in an effort to not hurt people that just purchased an upgrade or something, if you just purchased CS2, it's just as good as CS3 - just make a phone call.
In my case I went from Photoshop CS1 stand alone to CS3 Design Suite (which includes a fresh new copy of Illustrator, InDesign, Acrobat Pro) for only $499 by purchasing the CS2 upgrade and trading up. If I'd just ordered the same upgrade straight up to CS3 - it would have been $899.
If trading up CS1 PS standalone, the CS2 upgrade is only $160, where the straight up CS3 upgrade is $199.
Here's the official word on Adobe's site:
http://www.adobe.com/uk/support/service/postann.html
Just call the order number on their store site and ask about how a "Post Announce Upgrade" works. The person I dealt with said this offer was good until June on the CS products - don't know if that's official time though.