Only happens for connections that use FTS and only if you have configured it to use a dictionary (I believe there's no need to in case of an english body). But keep in mind that this means that you'll have to pay at least 0.5 seconds per search. If you do some google suggest style incremental searching on key press, you'll need to be faster than that.
So either use a persistent connection for full text searching (I'm connecting via pgbouncer for FTS-using connections) or, as karavelov recommended below, use http://pgxn.org/dist/shared_ispell/ which will load the dictionary once into shared memory (much less infrastructure needed for this one)
I'm thinking of a case where only maybe ~0.5% of queries will use FTS. I'm working on discussion software, and I'd like the discussions to be searchable, but realistically only a small percentage of queries will actually involve full text searching.