I have been studying this very issue (entire sanctification) and God has placed me for the time in a "Holiness" church (I never thought that I would be here). I have never heard this doctrine expounded/emphasized from the pulpit but it is the 'official' doctrine of the church.
As with many theological issues, a lot of confusion is introduced due to a disagreement about definitions. Justification is instantaneous and is likened to being "born again" and promises eternal life. The baptism of the Holy Ghost is instantaneous, and Glorification is instantaneous (in the twinkling of an eye). It is then understandable that some theologians would understand Sanctification would likewise be instantaneous and eternal.
Sinless Perfection / Entire Sanctification is a confusing term, but it is founded in scripture - 1 Thessalonians 5:23 - "Now may the God of peace Himself sanctify you entirely; and may your spirit and soul and body be preserved complete, without blame at the coming of our Lord Jesus Christ."
This much I know - our western church has become largely antinomian; therefore the "holiness" principle to battle every trace of sin is of great and admirable import! Grace has been overemphasized to the point of lawlessness. We should hate sin instead of excusing it! We should hate it not because we are seeking to 'earn' salvation, but because we want to be more pleasing to Him!
I know that there is a sanctification that is a process, for I am experiencing it daily. I have never reached the goal of being entirely sanctified but I do strive for it. I have not experienced a "lightening bolt" from heaven that forever separates me from the possibility of sin, and in truth I expect that many Weslyans confuse instantaneous sanctification with the baptism of the Holy Ghost....but I sure do admire those who are struggling to overcome sin - not in order to earn salvation, and not due to guilt or shame, but I sure admire those who are striving to please the Master!
As you walk out your faith today, remember that every sin has a price-tag! Can you even imagine trying to haggle with our Lord, who was tempted in the same ways that we are? Praise Him! Hallelujah!