We recently rolled out the Google Search Appliance at work, replacing the ageing (and dreadful) htdig (wikipedia link since the website appears to be down).
I’d previously put together a Firefox search plugin for htdig, but it wasn’t very good because the htdig search gave poor results and took ages to deliver them. Since we rolled out the GSA, I went to update the search plugin and found to my delight that Firefox 2 now uses OpenSearch for defining search plugins. So, ten minutes later and I had a working plugin, which was great. A week later, when IE7 RC1 came out I realised that IE has supported OpenSearch plugins for months, so I pointed it at my plugin, only to find that it didn’t work.
It turns out that IE doesn’t appear to support the nested Param element, although I freely admit that I haven’t checked the OpenSearch 1.1 specs to see if something changed from 1.0 (although a first pass of draft 3 doesn’t seem to include the Param element – I suppose the Firefox docs on the topic could just be out of date).