During the time of Jesus 'casting of lots' was a common means of 'seeking to make a choice' (Matthew 27:35; John 19:24; Acts 26:10). It is no surprise that we see the disciples employing the same means, even after initially praying (Acts 1:24-26).
A search through the entire book of Acts will reveal that this was the only time such 'questionable means' were used to determine God's will.
Casting of lots was common in the Old Testament, understandably, since they did not have the Holy Spirit so generously available to all people. Hence lots and other 'like means' were frequently used - Leviticus 16:8, Joshua 18:10; Nehemiah 10:34, 11:1; Proverbs 18:18.
After Acts 2, with the coming of the Holy Spirit, He was often credited with making of decisions - Acts 8:29, 39; Acts 11:12; Acts 13:2; Acts 15:28. God also used fellow Christians - Acts 9:10-17, Acts 11:27-30, to direct His people.
When making decisions today, we have four means at our disposal: the Word of God, the Holy Spirit, fellow Christians and sound guidance (which can come from other people trained in certain skills). By combining all of these means together we can safely reach godly decisions.
God overlooks times of ignorance (Acts 17:29-30). These were the times when our lack of intimacy with God allowed us to get away with 'casting lots' in order to know His will. As we grow in Christ He longs to lead us more directly (Matthew 7:7-11). This would account for the reason why you do not find the Apostles or any disciples casting lots for direction after Acts 1.
Nevertheless, being over confident is something we should guard against. People who go about attributing every decision they ever make - right and wrong, to the Holy Spirit, never allow anyone the chance of correcting them. The Holy Spirit is never wrong but He often gets blamed with the decisions we have made by human reasoning and 'casting lots'.