Ok, so I have been seeing a lot of people bash Jolteon on the Suspect Test thread and regularly on the usage stats threads. This just doesn't sit right with me. maybe it's because I have been a huge Jolteon fan since I first played Red. Perhaps it's because I used to rock him on PO in the days when he was UU. Or it could be that Game Freak gave him the perfect balance between cute little bunny/cat and awesome electric-spike fox. Whatever the reason is, I know for a fact that I'm hugely biased towards loving that little guy, and I don't think it's fair to call him a mediocre Pokémon. I decided to look at the potential of Jolteon in greater depth, though I have little experience using him in OU. In order to show you what I've found, I'm going to compare him to one of the premiere threats in the OU metagame: Tornadus-T.
TORNADUS-T
1. Base 120 STAB Hurricane with 30% chance to confuse.
2. Base 110 Special Attack.
3. Base 121 Speed + U-Turn to escape counters.
4. Regenerator, which allows for 33% health to be regained upon switching.
JOLTEON
1. Base 120 Stab Thunder with 30% chance to paralyze.
2. Base 110 Special Attack.
3. Base 130 Speed + Volt Switch to escape counters (sans ground types).
4. Volt Absorb, which allows for 25% health to be regained upon taking an electric hit (obviously not as good, but it's something).
So they actually have some pretty key qualities in common. SOme of the things that make Tornadus-T so powerful are also things that Jolteon has, not to mention he even has a better speed tier, though once you reach 121, there's not too much of a point in going higher.
There are, however, some things that make Tornadus-T better (obviously, I'm not saying that Jolteon is anywhere near as good as Tornadus-T, just that they're similar).
Negatives
1. Jolteon is affected by spikes.
2. Jolteon can't spam Volt Switch because of ground types.
3. Specs sets are good, but are risky because of ground types being immune to electric.
4. Volt Absorb is ok, but not nearly as helpful as Regenerator (though it does give him an immunity).
5. There are far more resistances to electric in OU than flying.
6. Jolteon doesn't have as good of a movepool/coverage.
7. Jolteon has much less bulk.
There are a few things Jolteon has over Tornadus though!
Positives
1. Jolteon is not weak to Stealth Rock.
2. Jolteon gets STAB on Volt Switch, making it more powerful than U-Turn.
3. Paralysis is, in my opinion, better than confusion due to the speed drop.
Naturally, as previously stated, Jolteon is nowhere near as good as Tornadus-T. However, I think it's unfair to call Jolteon mediocre, when it does have so much in common with the most threatening Pokémon in OU. Not only that, but a shocking number of rain teams have a huge weakness to electric types. Many have Politoed, Tornadus, Keldeo, Tentacruel, Gyarados, etc. Also, with hazards, it can actually kill Dugtrio, which I think is pretty funny, though only terrible players actually try to trap Jolteon with Dugtrio (its happened to my Jolteon before -_-).
So no, I'm not trying to say Jolteon is a top-tier threat or anything like that. Maybe it's outclassed by Thundurus-T, I don't know. I'm just saying that it has a lot of really great qualities that make it a strong Pokémon in this rain-infested metagame, and that people should give it more of a chance than they do currently.
EDIT: Look what I just found! Timid Jolteon outspeeds +1 Adamant Dragonite and Gyarados and can KO both with HP Ice and Thunder/Volt Switch respectively while holding only an Expert Belt. This assumes Multiscale has been broken, though.
252 SpA Expert Belt Jolteon Hidden Power Ice vs. 0 HP / 4 SpD Dragonite: 326-389 (100.92 - 120.43%) -- guaranteed OHKO
252 SpA Expert Belt Jolteon Thunder vs. 0 HP / 0 SpD Gyarados: 840-994 (253.77 - 300.3%) -- guaranteed OHKO