Do I need to get a reference letter from a postdoc host? I am currently a postdoc and will soon be applying for a faculty position in computer science. I am inclined to not ask my postdoc host for a reference letter when applying.

The reason I don't want to ask my postdoc host for a letter is because I have been a postdoc for less than a year and have mostly worked independently or with remote collaborators. So far I have only coauthored one paper with my host. (It's a good but not great paper.) Also, I am supported by a general fellowship -- i.e. I am not formally "tied" to my host, which means I don't think he feels strong "ownership" of me as a postdoc. It is not a true mentorship relationship.

I think my postdoc host would write a positive letter for me, but it would be weak for the aforementioned reasons -- he simply doesn't know me that well. I have other potential letter writers who would be able to write stronger letters.

What is worse? A weak letter from my postdoc host or no letter? Is this something I should try to explain on my application?

Any advice is greatly appreciated!
First of all: It seems you're on good terms with your host. Well, talk to him about this exact issue. He will probably sympathize and either let you in on drafting the letter, or at least agree with you in principle on what he intends to write. (And if he evades then you'll at least know there's something wrong.)


  What is worse? A weak letter from my postdoc host or no letter? Is this something I should try to explain on my application?


The answer depends a lot on whether the place/person you're interviewing for might talk to him over email/phone/Skype. 


If they will certainly talk to him, then a letter - good or bad - is not very meaningful anyway. He'll tell them what he wants to. So I wouldn't bother.
If they will certainly not talk to him, then your actual merits regardless of his opinion are likely to count for more than his letter anyway, so I'd get the letter from him just in case, and mention in passing that you worked mostly independently. I'm not 100% sure I'd add the letter to the application, it depends on the circumstances.
If you can't tell whether they'll call him up or not, I'd use the letter just to be on the safe side - assuming you actually get the letter in hand and don't have to ask him to send it to them directly (a weird custom that exists in some countries). Better this way then for them to call him up and for him to say "Uh, Dr. Foo? Umm, yeah, he was here, umm, he worked on... let me see.. it was some... stuff, I dunno. We wrote a paper together at some point, it was ok I guess. Not sure what he did exactly."


But frankly I have to say that it's not clear-cut. I, for one, would not put much stock in recommendation letters unless they said something exceptional.

One last point: Perhaps you should ask your host to focus on specific traits of yours, your skills or strengths in some things he's observed, in which case it won't matter all that much that you haven't worked a lot together.