the blockchain right now is not 600mb, its more like 400, excluding the index files. and that can be compressed to at least 80% of the original size.
and. 16 gigs should be good for a linux install and 2 more years worth of blockchain worst case.
so far bitcoin has been out for around 30 months and has only just reached about 400mb, 500 if you count indexes. thats 2.5 years.
My current bitcoin directory has 705MB right now.
A backup from the 18th has 612MB.
Another from the 14th has 592MB.
So, from 14th->18th, disk space increased by 20MB; that's 4MB/day.
From 18th->27th, another 93MB were saved, which means 9.3MB/day.
Of course it's easy to say "quit whining, diskspace is cheap", but when Bitcoin wants to enter the mobile/smartphone market, diskspace and traffic does matter.
Also, if you are an optimist and hope that Bitcoin will catch on and grow quickly, then the number of transactions will increase which in turn needs even more diskspace.
So, the faster Bitcoin grows, the bigger the storage requirements. This means the initial download/verify time will also increase and most likely anger new users.
Last but not least, when reaching a certain amount of transactions per second, the everyday John Doe simply won't have the bandwith to deal with the blockchain growth.