In a recent r/bitcoin's thread /u/thieflar claims that with 'a very nice machine' he was unable to finish validation of the ethereum blockchain and that the near impossibility of it is apparently an accepted fact even among ethereum's developers:

The developers of Ethereum know that this is an issue, they are fully aware that their network relies on trust at this point, and they don't even try to deny it.

/u/nullc comments with:

without being able to count on nodes verifying the history even ethereum seems unable to make a proposal complex enough to hide its insecurity.

I tested the truth of these statements - the result: full block-per-block syncing completed in 25 hours 25 minutes.

Software:
Parity at commit 2586eaef929cadcd5ebccdf2d484f1cf6bb14917, compiled with "target-cpu=native", performance options: --tracing off --cache-size 4096
Ubuntu 16.04

Hardware:
i7-6700K, 16GB ram, Samsung 850 EVO 256GB. Not bad but definitely not 'very nice' either.

To remove the network speed from the performance equation I downloaded the bare blockchain separately and synced the node from disk. As it's only 20GB at the moment there would be no noticeable difference.
23k most recent blocks were downloaded after that.

The fully synced node with all historical blocks recent state (ie. exactly like a full bitcoin node) uses 44.3GB.

Parity log.

Syncing from disk:
2017-12-30 20:15:50 Import completed in 87903 seconds, 4803128 blocks, 54 blk/s, 112578528 transactions, 1280 tx/s, 5273835 Mgas, 59 Mgas/s

Downloading the tip:
2017-12-30 20:33:53 Syncing #4803139 d21c…7352 0 blk/s 115 tx/s 5 Mgas/s 0 19 Qed #4803162 5/25 peers 365 KiB chain 72 MiB db 2 MiB queue 898 KiB sync RPC: 0 conn, 0 req/s, 0 µs
...
2017-12-30 21:33:43 Syncing #4825928 b3cb…6ec9 4 blk/s 720 tx/s 29 Mgas/s 0 15 Qed #4825945 7/25 peers 305 MiB chain 609 MiB db 3 MiB queue 3 MiB sync RPC: 0 conn, 0 req/s, 0 µs

Conclusion: any pc that can run a modern game can easily fully sync (no state snapshot downloading, only blocks) and run a full ethereum node.

^{edit: apparently reddit immediately deletes posts with links to mega}