The 49ers made Aldon Smith the seventh overall pick in the draft, and on top of that, a huge future piece in their 3-4 defense. Smith has the hurdle that most defensive lineman drafted to be a 3-4 OLB have: you know, actually learning the position. At pick number seven, it's not a matter of whether or not he will become a starter, it's just a matter of when. Smith will spend the offseason doing whatever he can to learn all of the facets of being a stand-up outside linebacker, with hopes of starting from day one.
Most will tell you that a realistic expectation is for Smith to not technically be a "starter", but rather a player who comes in on third downs to solely rush the passer. Actually, that's next to a guarantee that he'll be doing that as a "bare minimum." But Aldon Smith didn't get drafted to come in on third downs, he got drafted to be what Ahmad Brooks and Manny Lawson were supposed to, give or take a small quality or expectation.
So, if he were to progress and be a capable starting outside linebacker in the NFL, he still has to make sure he's more capable than the other players on the roster (duh, science!). Fortunately for him, the landscape of the 49ers outside linebackers is in a sorry, sorry state. Basically, Aldon Smith can start on either side, but he's more likely to be on the right side, where Parys Haralson is currently penciled in as the starter.
Not only that, but Ahmad Brooks and Travis LaBoy, despite uncertain futures with the team, could be in on things. Unfortunately for them, neither really seem like they're picking up any steam regarding a future starting job. Brooks has done nothing in the NFL other than perennially one step away from being a breakout outside linebacker, while Travis LaBoy really should be playing on the defensive line in a 4-3 alignment.
So, it really is down to Aldon Smith versus Parys Haralson. In regards to Haralson, he did look good in 2008 and 2009, but 2010 ... he really disappeared. His pass-rush arsenal consisted of only one or two moves that offenses keyed in on as he was the only real pass-rushing threat. There's just not much for him to offer in that regard, so he'll likely be outmatched from the get-go.
Fortunately for Haralson, he's decent in coverage. At the very least, you don't hear his name often, which means he's being trusted to cover and he's able to do so. That's the hurdle Aldon Smith needs to overcome. Can he do it? He's gifted enough athletically, and has showed a lot of ability to turn and rotate his hips effectively ... the tools are there, but smart money really is on him being slowly worked into it. The only sure thing here is the fact that, if Haralson does not perform, Smith will get playing time. It really is as simple as that.