I have stuck to OEM batteries. Now, I am sure that the "fakes" are, in some cases, as good the real deal - There is probably a good chance that they came out of the same factory as the originals, but....
Li-Ion batteries can be a bomb if they are not treated right and safegaurds are not implemented properly.
The recent recall of Nikon batteries is a testament to the fact that Li-Ion batteries can have problems - even the branded ones. It is reassuring to know that Nikon has been upfront on this one and has put the safety of it's customers first (and the possibility of a multi-million dollar compensation payout if someone was injured while Nikon knew of the problem and ignored it).
The questions that may be asked of the "fakes" are: If there is a fault will they be recalled? I doubt it. Some of the non genuine batteries may be afflicted with the same problem that caused the Nikon recall - but that is pure speculation. If the "fake" ruins the camera due to a fault, who is going to foot the repair bill? Nikon won't touch it (in terms of warranty) and I doubt that any of us would have much joy going after some unknown overseas company.
I do admit to there being a degree of FUD (Fear, Uncertainty, Doubt) in all of this, but thought I would lay out the cons of non genuine batteries. It is also the extreme (there is that word filter)
end. The Nikon battery recall was the result of something like 4 batteries... out of how many millions.
For my own use, I do not need more than one spare. I do not think that I have ever taken more than 600 shots in a day and I easily get that from one battery. I carry the spare, but I do not think that I have ever needed to use it. It is nice however, to have that spare "just in case" or to have a battery in the camera while the other is on the charger.
When I purchased the D70, I spent $2400 (IIRC) on the kit, $800 or so on the SB800, a couple of grand on lenses, more on a bag, CF cards, etc. Saving a few bucks on a battery did not make much sense at the time.
Cheers
PS. I still have 4 non genuine batteries for my old CP5700 and they were never a problem.