As far as timelines go, I'm a little confused. I am expecting that later this year, they will release the "Extreme Edition" Sandy Bridge chips, which I believe might be Haswell @ 22nm? Ivy Bridge is estimated to be released on Intel's tick-tock annual cycle, at CES 2012 next January, so I would assume that Haswell would be to Sandy Bridge, as Gulftown is to Yorkfield & Penryn.
You misunderstand: Sandy Bridge-E is not Haswell. Sandy Bridge-E is the pricey, high-end version of Sandy Bridge and it will indeed come out in Q3 2011. It will have more cores, more memory etc. etc., but the architecture will be more or less the same. After that comes Ivy Bridge in 2012 (or maybe at the end of 2011 if AMD manages to get something decent enough out to make Intel change their schedule) which is the 22nm die shrink of Sandy Bridge. Haswell is the new architecture after
Ivy Bridge. It is not scheduled until 2013.
What are your thoughts, folks? Does a Q9300 (Yorkfield @ 2.5Ghz x 4) warrant an upgrade to the i7-2600K Sandy Bridge?
If it's not broken, don't fix it. It doesn't make sense to upgrade unless your current part is limiting you in some way because there's always something better just around the corner (Bulldozer most likely in Q2 2011, then Sandy Bridge-E in Q3 2011, then Ivy Bridge). Sandy Bridge is a great laptop part because laptops are inevitably limited by battery life and SB is very good at this, but for a quad-core desktop it only makes sense to upgrade if you do something that pushes your Q9300 to the limit -- and in practice this means some sort of professional work because there are no games out that will be noticeably bottlenecked by the Q9300.