Its common practice for companies to match contributions with company stock. However, blatantly choosing your contribution to go into the company's stock is not the brightest idea. My company, for example, matches with company stock.... however, if you are above the age of 40, you can take the match and reallocate to whatever investment you choose.
In general, holding a large stock position in the company you work for is not a very good idea. The reason is that you already bear some degree of employment risk by the virtue of being employed by the company. Loosing your job and the compnay stock going down is likely to be an event that is highly correlated. So, if you buy stock in the company you work for, you are in effect, doubling down.
Many executives compensated by company stock are aware of this problem and there are several I-banks that have private client wealth management group that specially deal with this type of issue. Derivatives, put options, equity swaps and forward contracts can mitigate a lot of the risk if used appropriately.