I have trouble getting half steps, my sharps and flats. I know I can get them by half covering a hole, but is that THE way to do it? (I haven’t had any instruction on my whistles, I’ve just been figuring out things on my own or with websites like this!) Does anyone have some helpful fingering tips?
The Way to do it is whatever way works for you!
I tend to bend the half holing finger towards my palm, opening half of the hole vertically. I’ve also heard of some people opening up the half of the hole towards the bottom end of the whistle, but the other way works easier for me. I use this same technique to bend notes up too.
There are little tricks for certain notes.
for example on a D
C natural :
o
x
x
x
o
x
there are others
C Natural: OXXOOO on some whistles, second Octave: XOOXXO
Bb: XOXXXX, Second Octave: XOXOOO
G#: XXOXOX, 2nd octave: XXOXOO
These are the ones I use the CNatural has many variations. 
There is an “optional” tweak/modification for half notes in the form of a tiny speaker hole located just below the inner face of the fipple plug on the back side.
It was first developed by Arnold Dolmetsch for the Recorder and Flageolet to increase the pitch of each note by 1/2 tone and was called “An Echo Hole”.
This hole can also be placed below the voicing window within reach of an extended thumb. It must be tiny and about the size of one of the tiny double holes on the low note of a Recorder. If the hole is too large, it will “cancel” the fundamental register/octave and jump to the next one above.
Like any modification, it is modest in perfection and will be effective in only the first 2 registers. You may be able to find examples of this device at “The Recorder Homepage” as a “Tuning Device”(google it?).
Thomas Hastay.
What? 
A hole? As in, people put holes in their own whistles?
Do people ever do weird fingerings, like use a pinky somewhere (the small 4th finger)? I still have trouble with my tiny hands on my Bb whistle - the gap between the two bottom holes hurts my 3rd finger (ring finger).
I play both recorder and pennywhistle. Purists don’t like to add holes to whistles, but I feel people should do what works for them. Purists often say ”you might as well just get a recorder!” I like the simplicity of just six holes, but I also like the “lower maintenance” intonation of the recorder for the type of music traditionally played on it. I am used to playing the whistle “by the seat of my pants” while sight-reading or playing music by ear because I don’t have to put too much thought into fingerings. I actually prefer half holing, as it is my way of hitting incidentals on pitch. I have done it enough to “know where the note is” as far as half holing finger positions go. On the whistle, I have to really pay attention to get the C natural on pitch when cross fingering that note, among other things, so when I play music on the recorder, it seems I have good intonation out of habit and really don’t have to put much thought into it.
One more esoteric “half holing” I haven’t got down yet is placing the little finger partially across the end of the whistle to go from the D bell tone down to C#.
Ok, here’s a very very ignorant question - what’s the difference between playing a recorder and playing a tin whistle?
Very roughly, on recorder, in addition to the six fingers you would use to play whistles you use both pinkies and you have a thumb hole. Certain positions come as close pairs of holes so you can just cover one of the pair or both thus getting different notes. The fingering on a recorder changes from octave to octave more than on whistle. The recorder is fully chromatic; you can play in any key. The whistle is only semi-chromatic; you can play in any key in principle but few can do it in practice.
Some points about cross fingering on whistle. First, fingerings that work on one whistle might not work on another. The other whistle might respond to another fingering or to none at all for the note in question. Second, a cross fingered note might be noticably quieter than a standard note. You might not be able to rectify this by playing louder. Third, even if you can get a note by cross fingering, it might not be exactly in tune. In this case, you might be happy with it as it is—lots of us are happy sometimes with slightly sharp C-nats—or you might try to blow it into tune. The latter option might or might not be possible; it all depends on the whistle.
The hate mail
Wow, cool! Yeah, that is one frustration I have with the whistle, that it’s only semi-chromatic. I can maybe play in 3 keys on mine, but it’s rather laborious. Does whistle music change key in mid-song very often? Or switch from major to minor mid-song?
I’d guess that the most popular answer is: we avoid songs like that.
ITM usually doesn’t do that kind of thing. Key shifts are more in the realm of pop and orchestral music. Personally, I would love to whistle such compositions more easily, but it’s generally easier to play that stuff on the piano.
Right. I guess I hear such things in group arrangements, with fiddles and drums and everything. Maybe the whistler is able to take a moment and switch whistles?
Possibly…or possibly they switch to a key the whistle can play easily. Heck, you easily can get four keys (two major and two minor) out of any whistle, so it’s no big deal to modulate from, say, D to G or vice versa.
Redwolf
The person probably switches wistle mid-song