Does having machined brake surface on rims matter? I'm looking at getting a wheelset with disc hubs and rim brakes to run on my disc and non-disc cross bikes. There are stock wheels that have velocity a23 rims, which are a poupular rim brake compatible rim. However, the stock wheelset tend not to have machined brake surfaces.  

Is not having a machined brake surface a problem? 
Does it matter whether the rim is painted or anodized?  

Update:

It seems like some old heads seem to think that a machined sidewall was a marketing gimick made to stop brake squeal on new showroom bikes. Rivendell sell a lot of rim brake wheels without a machined surface.

Jobst Brandt via Sheldon Brown:
http://sheldonbrown.com/brandt/machined-rims.html

Rivendell (probably via Grant Peterson)
http://www.rivbike.com/kb_results.asp?ID=52
Rim walls are machined, if not for aesthetical or marketing reasons, to give the braking surface of rims most regular shape possible, removing small irregularities which could cause "hard spots" while braking, specially around the seam (spot where both ends of the rim are connected together during manufacturing).

Also, it seems to me that the residual grooved pattern improves braking power, most probably due to increased contact surface and possibly dirt clearance issues, without noticeable increase in pad wear, but I have no objective data to support this impression except a positive personal experience with a handful of machined-wall rims with v-brakes.

Hope this helps.