Sporadic-E peaks twice annually, in June and December, with the June peak normally more obvious and providing better and more frequent propagation in the northern hemisphere. Now that it's past mid-May, six meters is opening daily for Sporadic-E in many parts of North America, so if you listen carefully, there's a chance to work "skip" on six meters at least every week, if not every day. One problem is, the E propagation is indeed sporadic, and it's nearly impossible to predict -- and it sometimes occurs when nobody's around to take advantage of it.
We are now well past the peak of solar cycle 23, and the likelihood of much F-layer (worldwide) propagation on six meters is very slim. The most pronounced peak of the solar cycle for six meters occurred 1-1/2 years ago, in November 2001, when the band was open world wide for nearly 48 hours. I wouldn't expect that to occur again any time soon...maybe near the peak of cycle 24, which should happen in November 2009 or 2010.
Six is a very cool band, though, and long-distance propagation occurs by many mechanisms, not just F or E-layer skip. Six meters can provide very useful meteor scatter, aurora, TE (trans-equatorial) and all sorts of stuff enjoyed mostly by well-equipped stations using SSB or CW (or HSCW). A typical six meter station using 150W PEP output (SSB) and a 6 or 7 element beam at 40' above ground can usually work "DX" at least a few times each season by simply using the band.
WB2WIK/6