Obscuring mist makes no mention of speed and to my knowledge not being able to see more than 5 feet in front of you has no effect on your movement whatsoever, is this correct?
Difficult terrain, obstacles, or poor visibility can hamper movement. When movement is hampered, each square moved into usually counts as two squares, effectively reducing the distance that a character can cover in a move.
If more than one condition applies, multiply together all additional costs that apply.
From PHB p.163 or SRD.
The rules on Hampered Movement (PH 163) mention that "poor visibility can hamper movement [so that] each square moved into usually counts as two squares." Further, Table 9–4: Hampered Movement has "[d]arkness or fog" as the only examples of poor visibility (ibid.).
However, the Dungeon Master's Guide on Fog doesn't list reduced movement among its effects:
Whether in the form of a low-lying cloud or a mist rising from the ground, fog obscures all sight, including darkvision, beyond 5 feet. Creatures 5 feet away have concealment (attacks by or against them have a 20% miss chance). (94)
Further, the 1st-level Sor/Wiz spell obscuring mist [conj] (PH 258) doesn't mention reduced speed among its effects, either, nor does the 2nd-level Sor/Wiz spell fog cloud [conj] (PH 232).
With this in mind, this DM has never played that a creature that can still see—even only 5 ft. in front of it—has its movement hampered, nor has this player been in a campaign where the DM ruled that way. It's entirely possible that movement is supposed to be hampered in such circumstances—and that's supported by the rules—, but I've never had a DM put that particular 1 from the PH on hampered movement due to poor visibility and that other 1 from the DMG on fog together to get that particular 2.
Nonetheless,—maybe because hampered movement is mentioned explicitly by such effects,— a creature that's blinded or effectively blinded due to environmental circumstances—like being in absolute darkness through which the creature cannot see—does find its movement hampered.