And you thought the IRS was merciless!

Been studying the Acts of the Apostles for Sunday school (yes, it tickles me too, sometimes), and even the commentary I was using was repulsed by the tale of Ananias and Sapphira (chapter 5):

But a man named Ananias, with the consent of his wife Sapphira, sold a piece of property; 2 with his wife's knowledge, he kept back some of the proceeds, and brought only a part and laid it at the apostles' feet. 3 "Ananias," Peter asked, "why has Satan filled your heart to lie to the Holy Spirit and to keep back part of the proceeds of the land? 4 While it remained unsold, did it not remain your own? And after it was sold, were not the proceeds at your disposal? How is it that you have contrived this deed in your heart? You did not lie to us but to God!" 5 Now when Ananias heard these words, he fell down and died. And great fear seized all who heard of it. 6 The young men came and wrapped up his body, then carried him out and buried him. 7 After an interval of about three hours his wife came in, not knowing what had happened. 8 Peter said to her, "Tell me whether you and your husband sold the land for such and such a price." And she said, "Yes, that was the price." 9 Then Peter said to her, "How is it that you have agreed together to put the Spirit of the Lord to the test? Look, the feet of those who have buried your husband are at the door, and they will carry you out." 10 Immediately she fell down at his feet and died. When the young men came in they found her dead, so they carried her out and buried her beside her husband. 11 And great fear seized the whole church and all who heard of these things.

Yes, I bet it did! Why no chance to repent? Jesus said to forgive your brother who sins against you not seven times, but 77 times. The pitiless quality of the story has led some scholars, following a time-honored principle of biblical hermeneutics, to adjudge that a tale so repulsive cannot have been historically accurate or part of the original work.
Oddly, however, none of my three commentaries picked up on "lie to the Holy Spirit" and its echo of Luke 12:10: "whoever blasphemes against the Holy Spirit will not be forgiven." The Unforgivable Sin, in other words.
The parallel is more striking when we look at what use Luke has made of this saying. Mark, and Matthew following him, put the Unforgivable Sin in the context of Jesus's critics' saying that he casts out demons only because he himself worships demons; Jesus retorts that "a house divided against itself cannot stand" and invokes the Unforgivable Sin, which I believe is generally interpreted, by this context, to mean being so far gone as to attributed the good works of God to Satan.
But that's not what Luke—the author of Acts as well, recall—does. I don't want to dump all of Luke 12 here, but look at these snippets. The scene is set thus:

Meanwhile, when the crowd gathered by the thousands, so that they trampled on one another, he began to speak first to his disciples, "Beware of the yeast of the Pharisees, that is, their hypocrisy. 2 Nothing is covered up that will not be uncovered, and nothing secret that will not become known. 3 Therefore whatever you have said in the dark will be heard in the light, and what you have whispered behind closed doors will be proclaimed from the housetops.

How on-point is that with Acts 5? And then, immediately after verse 10:

11 When they bring you before the synagogues, the rulers, and the authorities, do not worry about how you are to defend yourselves or what you are to say; 12 for the Holy Spirit will teach you at that very hour what you ought to say."

That could be the epigraph for the book of Acts, where the Spirit is continually giving the apostles brave words in the face of hostile authorities.
And then Luke 12 goes into the evils of wealth and how one should give alms and share one's possessions, which is just what the early Christians in Jerusalem were described as doing in Acts 4, as the set-up for the Ananias story.
As one commentary (without picking up on the Luke 12 parallel) notes, the sin described in Acts 5 amounts to denying the Holy Spirit by denying its efficacy in the church.
There are certainly problems with construing the sin of Ananias and Sapphira with the sin against the Holy Spirit, if we take it that hiding part of the money indicated a lack of faith that God existed and would note the misdeed. Isn't that true of any sin committed in secret, in the hopes of escaping (earthly) punishment? Then again, the theology of Acts is not airtight in every respect. But perhaps the sin against the church itself—the word is used for the first time in Acts in the last-quoted verse from Acts 5 above—takes ab all-too-typical sin to the next level. At least, it must be said that had Luke desired to write a passage in his gospel to provide support for the just punishment of Ananias and Sapphira, he couldn't have done much better than Luke 12.