Well, first, Park Tools mentions loctite (blue/242/medium strength/non-permanent) first in their bit on installing bottom brackets (below).

The key things you are after are:

1) Making sure that the threaded joint doesn't loosen up in use. This is the function of threadlocker. Again, use the blue, medium strength, field serviceable, non-permanent stuff. Use blue, not red.

2) Making sure that the threads don't rust or corrode together and lock up or become weakened or non-serviceable. Grease or anti-seize work to prevent rust and corrosion. Loctite 242 is sold as a threadlocker and sealer, so I think it works for this purpose, too.

3) Making sure that in joints where both parts are similar metals, that they don't gall and cold weld (at least for bikes). So you're tightening a 316 stainless nut onto a 316 stainless bolt, and all of a sudden you can't turn the nut either way. The metals have galled and cold welded themselves, and your only next step is a hacksaw. 316 is notorious for galling, as is Ti. If you are threading a steel cup into a Ti frame, not so bad. If you are tightening a Ti nut onto a Ti bolt, USE ANTI-SEIZE. In non-bike apps, anti-seize also prevents high-temperature corrosion and keeps things like engine manifold and exhaust bolts usable. Anti-seize compounds have metal components (copper, nickel - even silver) that allow them to do their job.

The upshot is that threadlocker, grease, and anti-sieze all work. PTFE (Teflon(R) if it's Dupont's) tape (or better yet, PTFE paste - see Carroll Smith's comments on the difference in his book on fasteners) seems to work for some people. It may seal out water, but it doesn't protect the metal if water gets in. I say this as a PTFE "fan" - I used to work in the DuPont Plant that made Teflon(R) brand fluoropolymers like PTFE.

I'd use loctite, myself. In fact, I'm doing a build in the next month or so and will use loctite.

From Park:
Begin by preparing the threads of the bottom bracket. A thread locker may be used when the frame shell is steel and the cups are either aluminum or steel lockrings. A mild thread locking compound such as LoctiteŽ #242 that is considered “service removable” is preferred. This means that the parts are removable with normal tools, without taking extreme measures. If no thread locking compound is available, grease threads heavily or ASC-1 Anti Seize Compound. For more on thread preparation see Basic Thread Concepts.