This issue has been a bugaboo since the release of the Advanced Player's Guide, and more can be read about the issue in these Paizo message board threads from Aug. 2010, Aug. 2010 where you can (as I did) mark pretty much this exact question as a FAQ candidate, Oct. 2010, Nov. 2010, and Sept. 2012. Some on these threads agree with this answer, others with this one. Here's the unpopular reading. I hope it's useful nonetheless.
Using the feat Following Step to move 10 ft. can provoke attacks of opportunity
The feat Step Up has as its benefit:
Whenever an adjacent foe attempts to take a 5-foot step away from you, you may also make a 5-foot step as an immediate action so long as you end up adjacent to the foe that triggered this ability. If you take this step, you cannot take a 5-foot step during your next turn. If you take an action to move during your next turn, subtract 5 feet from your total movement.
Emphasis mine. When a foe adjacent to a creature with this feat takes a 5-ft. step away from the creature, the creature may take an immediate action to follow the foe (i.e. ending up adjacent to the foe) by...
- taking a 5-ft. step. On its next turn, the creature can't take a 5-ft. step, and, if the creature takes a move action to make a normal move, the maximum amount of movement he can make is reduced by 5 ft.
The feat Following Step has as its benefit:
When using the Step Up feat to follow an adjacent foe, you may move up to 10 feet. You may still take a 5-foot step during your next turn, and any movement you make using this feat does not subtract any distance from your movement during your next turn.
Emphasis mine. When a foe adjacent to a creature with both feats takes a 5-ft. step away from the creature, the creature may take an immediate action to follow the foe (i.e. ending up adjacent to the foe) by either...
taking a 5-ft. step. On its next turn, the creature can't take a 5-ft. step, and, if the creature takes a move action to make a normal move, the maximum amount of movement he can make is reduced by 5 ft.
moving up to 10 ft. On its next turn, the creature can still take a 5-ft. step and its next turn's movement isn't reduced.
There are reasons to employ either option—for example, the former doesn't provoke attacks of opportunity because it's a 5-ft. step and the latter allows the creature to get into a flanking position it couldn't quickly otherwise assume—, but, while a 5-ft. step doesn't normally provoke, 10 ft. of movement certainly can.
The ambiguity comes from interpreting the movement available through the feat Following Step as changing what a 5-ft. step is for the creature using the feat Following Step—that is, the creature's 5-ft. step becoming a sort-of 10-ft. step. But the feat Following Step makes no mention of such a change. The first clause of the feat Following Step ("When using the Step Up feat to follow an adjacent foe") references not the feat Step Up's 5-ft. step but, instead, what the feat Following Step means when it says follow an adjacent foe; that is, a creature with the feat must end its movement adjacent to the foe that moved away, a fact otherwise unmentioned by the feat Following Step.
Also noteworthy is the feat's Following Step's normal entry, which says that...
You can only take a 5-foot step to follow an opponent using Step Up.
This seems to differentiate the 5-ft. step the feat Step Up allows a creature to take from the move up to 10 ft. that the feat Following Step allows a creature to take, the normal entry pointing out, essentially, that a 5-ft. step isn't 10 ft. of movement.
Make creatures happy with house rules
Under this reading, the feat Following Step is useful only in niche situations, usually only being not much better than DM_Blake's fictional feat Scratch Your Head ("Benefit: None, except that your head feels wonderfully itch-free all day"). Making the feat do something other than what's written will brighten the day of any sad creature slogging organically through the Step feat chain.
- A house rule making the 10 ft. of movement from the feat Following Step not provoke attacks of opportunity makes the feat substantially better but still not good. However, many feats aren't good, so that's not really that big of a deal.
- Alternatively, a house rule allowing a creature to employ both the 5-ft. step from the feat Step Up and the 10 ft. of movement from the feat Following Step when a foe takes a 5-ft. step would also be an improvement, allowing a creature, for example, to block the path of a foe of no more than Medium size.
- Combining the above house rules to allow a creature with both feats to follow for 15 ft. without provoking attacks of opportunity when a foe takes a 5-ft. step would likely make the feat actually good and open up some interesting tactical options.
This GM has not playtested these house rules, this information instead gleaned from having read a lot about the feat Following Step.