I've personally never tried it in the neck position, since I previously didn't care much for neck pickups. I actually use neck pickups nowadays, but I have yet to try the 81 there.
However, I'm finding it increasingly hard to recommend the 81 at all - unless the "81 sound" is what you want. It works well for high-gain situations, but after I took some time to listen in carefully, I realised that it's a damn bland pickup. I currently only have one guitar with the 81 - my single humbucker Flying V, which I haven't played in months (it's back at my parents' house). Its clean tone always kinda sucked, while it ruled for high-gain rhythm playing. I never really gave it much thought until recently.
Go to
www.emginc.com and listen to the sound samples (unfortunately they only have samples from bridge position on those pickups). Compare the 81 to the 85. A world of difference - especially on the clean channel. Where the 85 sounds groovy, the 81 sounds dead and dry as a bone.

Awful guitar sound in the sample for the 81 on clean - I'm kinda wondering if they were playing on old strings when they recorded it. You could probably EQ the mids up a bit to compensate tho'. I've heard that some studio techs like the flat signal of the 81, because it's supposedly easy to add color to it with EQ and make it suit the mix.
I'd rather recommend the 85 for both the bridge and neck positions, even though I tend to like bright and clean sounding neck pickups (85 is darker and a bit dirtier than the 81). I'm currently using a 58 (which is the precursor to the 85), and it sounds fabulous in the neck position - for both clean playing and distorted leads. The only thing it would need is a teensy bit more high end IMO.
However 2: I read a review at one point (probably at the J/C forums), with someone saying that he thought the 81 sounded pretty neat in the neck position. I also recall him saying that it sounded kinda raw and bluesy (think Kirk Hammett's solos), but I don't remember him saying anything about its clean sound.
Hmm...maybe I should've just narrowed this post down to "I don't know". I don't like to throw biased views at people. Maybe you'll like it, maybe you won't. Sorry I can't help you more.
'bane