I do not auto-squelch because of a single blind invite. I do auto-decline, though, as many others here seem to do.

Blind invites could be annoying if I was in the middle of a fight, but I can't remember the last time that happened. I would definitely react to that with a pointed tell.

Azmodeus1: Yes, you might find it easy to spam invites that way. As Cardtrick says, though, be aware that continued use of spamming blind invites will annoy a lot of people, and might make it harder to get into groups at higher levels. Try to use the LFM system, it really does work here in DDO, and doesn't take all that long to set up.
Sending tells is fine, too, IMO - as long as they're polite and fairly understandable.