Suit yourself but it does work.
Code:
$ youtube.sh youtube.com/watch?v=LHelEIJVxiE
46 1080p WebM vp8
37 1080p MP4 h.264 high
45 720p WebM vp8
102 720p WebM vp8 3D
22 720p MP4 h.264 high
84 720p MP4 h.264 3D
44 480p WebM vp8
35 480p FLV h.264 main
43 360p WebM vp8
100 360p WebM vp8 3D
34 360p FLV h.264 main
18 360p MP4 h.264 baseline
82 360p MP4 h.264 3D
5 240p FLV h.263
36 240p 3GP mpeg4 simple
17 144p 3GP mpeg4 simple
usage: youtube.sh [ITAG] URL
$ youtube.sh 37 youtube.com/watch?v=LHelEIJVxiE
--2013-01-20 20:20:21-- http://r9---sn-q4f7dn7r.c.youtube.com/videop
layback?mv=m&source=youtube&sparams=cp%2Cid%2Cip%2Cipbits%2Citag%2Cra
tebypass%2Csource%2Cupn%2Cexpire&cp=U0hUTVdQV19JTUNONF9PSkFHOnFoNGhZS
WJkcWZm&ms=au&ipbits=8&sver=3&expire=1358759643&mt=1358734810&id=2c77
a5108255c621&itag=37&upn=TbYQqBTiOpY&newshard=yes&ip=99.109.97.214&ke
y=yt1&fexp=920704%2C912806%2C922403%2C922405%2C929901%2C913605%2C9257
10%2C929104%2C929110%2C908493%2C920201%2C913302%2C919009%2C911116%2C9
26403%2C910221%2C901451&ratebypass=yes&signature=2C8615065314DC13FA54
5E057ACAA37C55004942.85F61420F91DCDCBACACDF881B06DFBFC9938402
Resolving r9---sn-q4f7dn7r.c.youtube.com (r9---sn-q4f7dn7r.c.youtube.
com)... 173.194.24.142, 2001:4860:4002:4::e
Connecting to r9---sn-q4f7dn7r.c.youtube.com (r9---sn-q4f7dn7r.c.yout
ube.com)|173.194.24.142|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 17891401 (17M) [video/mp4]
Saving to: `a.mp4'
100%[===========================>] 17,891,401 1.37M/s in 12s
2013-01-20 20:20:34 (1.37 MB/s) - `a.mp4' saved [17891401/17891401]