I believe in keeping options open, or at the very least not burning bridges, when there is a reasonable level of effort on the part of the recruiter. If the message is obviously untargeted, or the recruiter is trying to get around the normal channels (ie, sending an LI connection and throwing in a "check this dope opening!1!" message in the invite) then those do not warrant a reply and get hit with the spam hammer.

Otherwise, I have a standard reply that I just copy-paste in to be human about it and make it exceedingly quick. True, 99% of the messages are not going to interest me, but I think everyone deserves to be treated fairly if they've made an effort. You never know who you might run into a second time when you're in need. It goes something like this:

> Hello [Recruiter],

> Thank you for reaching out, I appreciate it! Unfortunately I'm not looking to make a jump right now, but I wish you the best of luck in finding some great candidates.

> Thanks again,

> Joshua

I'll make tweaks to the standard message when warranted. For example, recently the CTO of a large-ish web property was the one who made the direct contact herself, instead of just a recruiter or hiring manager. I wasn't interested, but that obviously warranted a more thoughtful response. Other times, if the recruiter actually has the wherewithal to (shock!) include salary details and actual information I often complement them on that fact, to encourage the behavior more often in the industry.

In general, true, it can be annoying to get many an unsolicited and uninteresting offers. But on the other hand, what a great privilege we have to be in a field where we are in such demand that people are pinging you left and right; we should count our blessings! :)