My experience is that there is a noticeable performance increase from 512K to 1GB. Not so much from 1GB to 2GB. It'll certainly put much less demand on the ssd
for swapping. Memory is cheap so it makes sense to go for the 2GB upgrade. If you're patient, you can eventually find a 2GB module for less than $20 shipped. Keep tabs on slickdeals.net
Getting Ubuntu to recognize the upgraded RAM wasn't a problem for me. Just needed to let it do the automatic package upgrade and it upgraded the new kernel.
Web surfing will be fine with 4GB ssd
. Not sure about rosetta stone and wine, but I'm guessing it'll probably be okay, especially if you make use of a SDHC card.