[pjdorrell]

Be aware that there is a backlog of "secret" patent applications in the US, where the patent application can be kept secret until such time as it is granted, at which point the easy invalidation described by Joel is not allowed.

For example the Twitter patent was granted, even though there is prior art (mine), and even though I submitted my prior art as soon as I found out about the patent. But I got a reply along the lines of "too late, the patent has been granted". It turned out that the application was kept secret until it was granted, thus guaranteeing protection from any prior art not already known to the patent office employee assigned to that patent.

The "new" US patent laws require an application to be made public after 18 months, but there could be thousands upon thousands of older patent applications benefiting from the secret option.