How to become a committer
There are two types of commit access: full and partial. Full means anywhere in the tree, partial means only in that committer's specific area(s) of expertise. The processes SharpSvn uses to get commit access is copied from the Subversion community.
How full commit access is granted
After someone has successfully contributed a few non-trivial patches , some full committer, usually whoever has reviewed and applied the most patches from that contributor, proposes them for commit access. This proposal is sent only to the other full committers -- the ensuing discussion is private, so that everyone can feel comfortable speaking their minds. Assuming there are no objections, the contributor is granted commit access. The decision is made by consensus; there are no formal rules governing the procedure, though generally if someone strongly objects the access is not offered, or is offered on a provisional basis.
The primary criterion for full commit access is good judgment.
You do not have to be a technical wizard, or demonstrate deep knowledge of the entire codebase, to become a full committer. You just need to know what you don't know. If your patches adhere to the coding guidelines, adhere to all the usual unquantifiable rules of coding (code should be readable, robust, maintainable, etc.), and respect the Hippocratic Principle of "first, do no harm", then you will probably get commit access pretty quickly. The size, complexity, and quantity of your patches do not matter as much as the degree of care you show in avoiding bugs and minimizing unnecessary impact on the rest of the code.
How partial commit access is granted
A full committer sponsors the partial committer. Usually this means the full committer has applied several patches to the same area from the proposed partial committer, and realizes things would be easier if the person were just committing directly. Approval is not required from the full committers; it is assumed that sponsors know what they're doing and will watch the partial committer's first few commits to make sure everything's going smoothly.
Patches submitted by a partial committer may be committed by that committer even if they are outside that person's domain. This requires approval (often expressed as a +1 vote) from at least one full committer. In such a case, the approval should be noted in the log message, like so:
Approved by: bert
Any full committer may offer anyone commit access to an experimental branch at any time. It is not necessary that the experimental branch have a high likelihood of being merged to trunk (although that's always a good goal to aim for). It's just as imporant that the full committer — all the full committers, actually — view such branches as training grounds for new developers, by giving feedback on the commits. The goal of these branches is both to get new code into Subversion and to get new developers into the project.