This is the first time...

Consider these two structures:

1) This is the first time I've done something.
2) This is the first time I'm doing something.

Some native speakers told me that #2 is always unnatural, no matter if you are talking about something that is still happening. Others say it's ok. Do you think sentences like "This is the first time I'm seeing this" are unnatural? Do you ever use the present continuous with "This is the first time"?
State if you are talking about British English, American English, or any other variety if possible.
Thanks.

On your way to a demonstration/protest/lynching/etc., you could easily say:

"This is the first time I'm doing something like this."

[US English]

<<
1) This is the first time I've done something.
2) This is the first time I'm doing something.
>>

#1 is for when you have just completed the task/activity and it was the first time.

#2 is while the task/activity is still ongoing.

Either is fine, but they do not exactly mean the same thing. Time is the difference.