You can do a cross-platform upgrade from CS3. DO be aware that Adobe requires users who wish to upgrade to CS6 (we assume it will be released in 2012) to be current, which means owning CS5. You can upgrade to CS5 until December 31 at a reduced cost. Bottom line, this means you are "on the chain gang" and will need to upgrade every version, or lose the right to upgrade pricing. I personally think this stinks (and so does Scott Kelby, apparently) but it is the way it is.
It really depends on what you use now. I use mostly Photomatix, Nik's Viveza and Silver Efex; only occasionally CS5. I have Elements 7 but never use them (anyone wants them?)
